Powder Burn and Pressure Relationship

[303Guy]

Does anyone know which of the slower powders are less sensitive to initial chamber pressure i.e. burn better at lower pressures?

As in using a slower powder for a gentler launch without suffering the penalty of inconsistent burn or ignition?

[DrCaveman]

Im interested here. More i learn about caressing the base of the boolit, the more i like the slower powders. And the more i try them the more i like them. But like you ive yet to find one reach its potential at anything less than a nearly-full load.

Since you are a pretty filler-happy guy i assume you are looking for a load that doesnt need one. So am i.

Ive been considering requesting a chart which lists optimal pressure for each powder. Most ive found seem to have a window of excellence, some powders give a broader window than others.

I dont test or use nearly enough powders to come up with this chart, but ill bet there is plenty of collective wisdom here to pull it off

[uscra112]

All I know is that the modern Schuetzen guys seem to have been attracted to AA #9, AA1680, and Alliant MP300. Not especially slow, but they do give very consistent SD in 15K psi loads for plain base boolits. Some of these guys can shoot 1/2 MOA groups at 200 yards, so there must be something in what they say.

Me, I can only vouch for #9, but have managed to obtain MP300 and 1680 for the coming test season.

I use Varget by choice for full-power (40K+ psi) loads in 5.56 and .30-30 with J-warts, but I've also read a report here that some guys are getting it to work very well at under 20,000 psi, so maybe that's a possibility? Hard for me to test - I'm down to my last half-pound, and can't find any to buy anywhere.

Phil

[Doc Highwall]

There is more to it then just a optimum burning pressure. A gun is basically a simple piston engine, bore verses stroke = volume.

The larger caliber guns drop pressure at a faster rate then a smaller caliber. You also have to take into consideration the sectional density and bearing surface of the bullet on the rifling.

How about a 22-250 Remington that has a greater case capacity then a 30-30 Winchester, or take the 30-30 Winchester and neck it up to .375 diameter and see what it does to the time pressure curve.

Lots and lots of variables come into play in how the pressure rises and then falls affecting pressure.

[303Guy]

Exactly! I have what could be termed a classic example. My 22 hornet - I loaded it with Lil'Gun which is reputed to require a mild primer (pistol) and a stiff crimp to get consistent ignition and burn. A hot primer pushes the bullet out before full ignition resulting in irregular pressure. I used an unsized case and neck that required a paper cup to take up the clearance with the bullet. I overcame the burn problem by using heavier bullets (55gr) and a compressed powder charge. I was effectively using the powder in its compressed state plus a heavy bullet to create sufficient back-pressure to burn well. And it burned very well indeed. 2740fps from a hornet with 55gr j-words! Pressures were a little higher than a hornet is supposed to have but the action was designed for a 222 so I was only concerned about the cases holding out and they did. So, a progressive powder being made to work by using tricks. Pretty much what corn filler does (I think). But the idea is to find a powder that burns better than the rest at lower pressure but still gives a gentle launch and high velocity at low peak pressure. A tall order but no one powder is the same as another so one of them out there is going to be better than all the rest for this application. I'm trying W780 and W748. I have tried H4350 and it did work but it kinda sorta peened the cr*p outta the boolit bases.

66058

Those kernels are lying in the impressions made by them. There some visible indentations without kernels lying in them too. I did try a card wad which did help but I found Dacron with W748 the best of those I'd tried at that time.

[44man]

I like Varget. I even found it works perfect in 10" barrel 7R and 7BR with light 120 gr bullets ("J" words) after Hodgdon told me it was too slow. It is the ONLY powder that gave me super accuracy from the fast twists with the light bullet. Both guns were made for heavy.
It is true what Doc said. Then most slow powder needs high powder amounts and can't be reduced much. That increases all pressures from start to finish.
Might be an idea to look at load charts and find the powders that show more reduction ranges.

[uscra112]

If you want to play with options, open yer wallet and buy a copy of Quickload. I feel like a man born blind that has been given sight now that I have it.

The trick of using pistol primers in the Hornet holds for all powders. The best (lowest pressure) primer is the Remington 1 1/2, by a significant margin. Every so often somebody builds a test rig to measure the explosive pressure of primers, and every time I read a report the Rem 1 1/2 is the lowest.

The earliest such test I know of that was popularly reported was documented in a 1930s American rifleman. The test was to put a closefitting brass rod in the bore of a rifle, and launch it vertically with the primer. (No powder, obviously). A second operator eyeballed the height against a scale pasted to the side of the house. Redneck engineering at its' finest!

[Rocky Raab]

To address the original question: In general, you'd concentrate on single-base powders with little or no ignition suppressant. The complication is that a slow burn rate is often a slow ignition rate, because the way that powder engineers achieved a slower burn was to layer on more and more ignition suppressants. The harder it was to light, the longer the interval before all the powder was lit - and therefore the "slower" the burn time.

Today, powders are much more sophisticated. They can be made in layers with varying chemical properties in each layer to control the ignition and burn time of each kernel. That's essentially how modern spherical powders are constructed - and why such new ones as LilGun and AA#9 can be made to ignite easily but burn slower than they otherwise would if they were monolithic.

[44man]

If you want to play with options, open yer wallet and buy a copy of Quickload. I feel like a man born blind that has been given sight now that I have it.

The trick of using pistol primers in the Hornet holds for all powders. The best (lowest pressure) primer is the Remington 1 1/2, by a significant margin. Every so often somebody builds a test rig to measure the explosive pressure of primers, and every time I read a report the Rem 1 1/2 is the lowest.

The earliest such test I know of that was popularly reported was documented in a 1930s American rifleman. The test was to put a closefitting brass rod in the bore of a rifle, and launch it vertically with the primer. (No powder, obviously). A second operator eyeballed the height against a scale pasted to the side of the house. Redneck engineering at its' finest!
What have I said forever about the .44 doing better with standard primers? 303 even mentioned it. It is true, never push out a boolit with primer pressure first before good ignition.
I never made much funny tests, just shot to find accuracy. Primers are so important that everyone needs to test and never just read stuff.
Some cases are just too small for primer pressure. Some are too large for primer heat. Please experiment.

[dverna]

I hope you guys are right about Varget. I bought 16 lbs before the crazies hit to work up loads for a 200 gr .308. This is an interesting thread. A well respected gentlemen on this site has provided some feedback and he thinks I will need a slower powder (4831SC). It did not surprise me as it seems there is a lot more success with using slower powders with cast bullets in rifles. But I cannot find any 4831SC powder anywhere. I have one more place to visit next week to see if I can snag some to experiment with.

Like many casters, I started with fast powders in cast "target" loads and our history can work against us. Regrettably, the old Lyman loads for rifles also tended more to "reduced" loads with smallish charges of shotgun type powders. More history to overcome.

One option may be duplex loads but I am pretty sure I do not want to go there. They are probably OK but probably is still too risky for me. I will settle for less velocity.

One of the things I did was obtain a rifle with a 26" barrel. For a "target" gun made to shoot cast this will allow more time for the burn and better use of slower powders. I realize pressure is not be linear as the bullet moves down the barrel but it makes sense that if 30,000 PSI acts on a bullet for 26" of travel, it will be traveling faster than if it accelerated over only 20".

One thing to bear in mind is that a powders (like Varget for example) have a wide range of published pressure use in cartridges other than the high intensity rounds we may be using. For example Varget is listed for loads in the .30/30 at pressures as low as the high 20's and in the .45/70 with loads generating as low as 16,000 PSI. But it gets most of its "press" with higher pressure loads in the .223/5.56 and .308. This tells me it can be loaded down with some safety if case volume is not reduced too much.

We are saddled with published data that tries for maximum velocity with jacketed bullets. There is no marketing drive to test loads at the low pressures that are more suitable for cast bullets in rifles like 7mm/08, .30 cals, 8mm etc. Yet we may still be able to shoot those powders safely at below "optimum" loads just as 44man proved with his experience when he ignored the factory recommendation that "it was too slow". It was not too slow for his loads.

[303Guy]

Hodgdon:

110 GR. SPR FP Hodgdon Varget .308" 2.415" 34.5 2365 27,200 CUP 38.0C 2572 31,900 CUP

But it gets better


110 GR. SPR FP Hodgdon BL-C(2) .308" 2.415" 36.0 2351 24,500 CUP 39.0 2526 25,400 CUP

[303Guy]

More interesting load data from Hodgdon.

303 Brit

180 GR. SIE SP Hodgdon Varget .311" 3.075" 37.0 2282 38,200 CUP 41.0 2440 43,400 CUP


180 GR. SIE SP Hodgdon BL-C(2) .311" 3.075" 41.0 2395 37,100 CUP 45.0 2563 43,000 CUP

I couldn't find any BL-C(2) so I got some W748. It's OK but doesn't produce the velocities with the low pressure of BL-C(2).

45-70

300 GR. CAST LFP Hodgdon Varget .458" 2.465" 45.0 1599 17,800 CUP 55.0 1880 20,600 CUP


300 GR. CAST LFP Hodgdon H4895 .458" 2.465" 45.0 1572 14,400 CUP 51.0 1703 15,500 CUP


385 GR. CAST LFP Hodgdon H4895 .458" 2.505" 35.0 1280 11,900 CUP 42.0 1526 23,100 CUP

H4895 looks like a winner so far.

Thanks for all the great tips!

I'm going to go play with primers now. :D:)

[44man]

I also like 4759 for many guns but ran into a failure to ignite in my 45-70 BFR. I went to a heavier boolit and reduced the load 1/2 gr because I had no load info. Boolit and powder just went into the bore. Increasing the charge cured it and it is accurate.
Now this is a very easy to ignite powder yet it failed.
I also used Dacron filler in the loads but it did not help.
There is so much I don't understand or can solve because stuff happens we don't expect. Who in the world would expect a small reduction of 4759 to fail? Surely not me!

[303Guy]

I don't suppose you would have tried it again after the failure to see if it always fails like that (I know I would not have)?

I keep coming across two powders that behave differently in different cartridges and at different load levels also with different bullets. BL-C(2) and W748 are two I've compared. CFE 223 is a new powder that is comparable to BL-C(2) in that it produces high velocity at lower pressures in a wide range of cartridges.

So I'm thinking of finding an available new or modern powder to try out. Sometimes BL-C(2) is available here but H4895 would do too but I'm not sure that these are different enough from W748. So far I haven't found a listing of W748 showing how low in pressure it can go and for me to test it I would need to chrono it. I have taken it as low as 23grs in my Brit but that was with filler and a heavy boolit and only into the 'test tube' so it doesn't mean much. Powders are not cheap here down under so to buy a can then not need it is silly but hey, one can fins an excuse to use it, right?

I noticed that W748 is only indicated for heavier bullets but is similar in performance to Varget, BL-C(2) and H4895. Harder to light up maybe?

[mpmarty]

I don't much care for blc-2 as it doesn't burn clean for me unless I really boost the load. Varget and H335 are a couple of my favorites.

[44man]

I don't suppose you would have tried it again after the failure to see if it always fails like that (I know I would not have)?
QUOTE;
Not for a second and you are right. Once is enough and scares me silly. Just what if it would have lit off up in the barrel?
I have limits and it took a month before touching the trigger on my BFR 45-70 but I was still on my own. Rifle loads were out of the question for a short barrel. Nothing but flash at the muzzle and unburned powder. I actually poured unburned powder from the brass.
If anyone thinks all powder is consumed at peak needs beat with a large stick.
Some want a .500 S&W with a 2" barrel thinking it has more power just because it is big. They say using slow powder is still best. What planet are they from? It is recoil and muzzle blast only that they think is power.
So much powder energy is wasted in the air.

[Doc Highwall]

I was amazed at how I could see a secondary powder burn/pressure spike using a strain gage with AA5744 in my 308 Winchester. I will have to figure out how to post a picture of it from my lap top.

[303Guy]

I fired a Federal large rifle primer with an empty case and a fairly loose patched boolit. The boolit stayed inside the throat but bumped out quite easily. There are leade marks on the patch but no impressions. There was virtually no grip on the boolit.

[uscra112]

If you go to the threads on the S.E.E. that have been here on CB, there's finally a rational explanation that centers around the primer explosion pushing the j-wart into the throat, and a millisecond or so later the charge goes off, with the j-wart acting as an obstruction. The clue was a double peak in the pressure curve observed by a lab testing some 6.5mm round. Worst with reduced loads of a hard-to-light powder, and a magnum primer has been used to get it to light.

ON THE OTHER HAND - Warren Page wrote in the '70s that, when using slow-for-case-volume powders in benchrest rifles, jamming the j-wart into the leade was actually the right thing to do, to make it stay put while the powder burn built pressure. Just to opposite of what we've been told by umpteen experts for umpteen-and-fifty years. But maybe it's OK when the j-wart is a lightly built HP benchrest bullet, and not OK when the bullet is a long skinny 6.5mm cruise missile?

Finally - I've often slugged a throat by launching a boolit into it using just the primer. In large cases like the 7.5x55 I've been messing with recently I had to add 0.3 grains of Red Dot, but in small cases like .357 Max, a magnum primer did it just fine. No crimp of course.

[uscra112]

Varget and H4895 are both stick powders, which are said to light easier due to have less aggressive deterrent coatings. If that means anything. And 4895 has always been one of the canonical cast-bullet powders in the .30-06, going back to the '50s, if what I read in the old sources is accurate. It's a good deal slower than Varget.

The comments about light loads of Varget were on a thread here regarding the 7.5x55, my remembery is trying to tell me.

[303Guy]

H4895 powder was chosen because it is the slowest burning propellant that ignites uniformly in reduced charges. For years
H4895 has been the top choice of cast bullet shooters.

H4895 is faster than Varget.

[uscra112]

You are right. I should make sure brain is engaged before putting fingers in gear. It's right next to Varget in the Quickload database, but it does come first. As punishment I shall let that post stand.

[BAGTIC]

What burn there is will occur in the first few inches of bullet travel no matter how long the barrel as long as peak pressures get high enough to ignite the powder. The higher velocities of longer barrels is from their greater expansion ratio not their greater propellant burn.

Most powders have about the same energy per weight and produce similar amounts of gas. Use of a larger case will allow a greater volume of powder (more gas) to be used at a given peak pressure. For example if one charge burns 20 grains at peak pressure of 30 kpsi and another charge burns 40 grains at the same pressure the latter will produce more gas volume and will be able to maintain the gas pressure longer. The longer the pressure can be maintained the longer the bullet continues to accelerate.

Barrel pressure does not stay anywhere near constant over any distance of bullet travel much less 30 kpsi to 20 inches our 26 inches.

A QL check using a 30-30 with a 170 gr GC Lyman RN bullet and 30.3 gr IMR4895 shows 2000 fps @ 20" and 2100 @ 26 ". WOW. A whopping 100 fps difference. The increase in powder burned 20" vs 26" was 3 %. WOW again. Peak pressure 30 kpsi occured at 1.4 inches and decreased to 20kpsi (5 inches), 12 kpsi (10 inches), 9 kpsi (15 inches), 6.2 kpsi (20 inches, 4.65 kpsi (26 inches). If we can not maintain 30,000 psi from the peak at 1.4 inches out to 5 inches how do we expect to maintain it to 20 or 26 inches?

The advantage of slower powders is not longer burning times. It is the ability to burn greater quantities of powder, producing greater quantities of gases, without exceeding peak pressure limits. Their importance is that they are 'slower' in terms of slower pressure rise rate. Once peak pressure has been reached that advantage disappears. In fact a powder that has a faster burning rate after peak pressure has been reached would yield better performance since that gas would have longer to act on the base of the bullet. Better to have that energy released after 5 inches of bullet travel than after 15 inches.

[Larry Gibson]

Doc makes several very good points; having measured and observed the time/pressure curves of numerous powders in numerous cartridges the last few years I have to certainly agree with: primarily the expansion ratio of the cartridge has a lot to do with how well a slower powder burns at what psi levels.

Assuming the "slower burning powders" is refering to rifles I have found the following medium to slow burners to work well (read that ignite and burn reletively evenly) at low psi (down to the 20,000 psi level); 4895 (I prefer H4895), Varget, 4064, RL19, 4350 (I prefer AA4350), RL19, H4831 (I prefer H4831SC) and RL19. The exact bottom end of that level is very dependent on the exapnsion ratio, bullet weight and case volume (load density). The use of a dacron filler when load density is less than 80 - 85% greatly improves the ignition and efficiency of the burn.

Like Doc I also sometimes have secondary spikes with some cartridges with some powders, even faster burning ones. It's not the gun used or a defect in the gauge mounting as other loads give smooth time pressure curves. I've not yet figured it out......probably time to call Dr. Oehler?

I'm sure there are others out the but I've not tested all of them so can't say. The above listed powders are generally readily availble, work well in a wide range of cartridges with medium heavy to feavy cast bullets so I've not had a need for a lot of other testing so far.

Larry Gibson

[303Guy]

The advantage of slower powders is not longer burning times. It is the ability to burn greater quantities of powder, producing greater quantities of gases, without exceeding peak pressure limits.
Actually, with rifle powders the burn continues past the peak pressure point of the curve and slow powders burn quite a ways down the barrel. Maybe not all the way down and maybe not even half the way down but further than just the peak. It has been shown that a longer barrel will burn all the powder while a shorter barrel with the same loading will leave unburned kernels (that's with a specific load and powder, not any or all loads and powders). Increasing the powder charge with the specific loading will often burn all the powder. Point is some powders behave differently to others.

My uncle was an armourer in the dessert in WWII and said that after a 50 Browning machine gun shoot at the range they would sweep up heaps of partially burned powder from in front of the guns.


Like Doc I also sometimes have secondary spikes with some cartridges with some powders, even faster burning ones.

That secondary pressure spike has been lab tested and it's not barrel harmonics or some such. They went so far as to pack the barrel with sand bags to dampen vibration and that spike was still there.


A conclusion by some was that PressureTrace picked up barrel harmonics. In an attempt to prove this theory one shooter even hung a bowling ball off the end of his barrel, but of course there was no change.
Public debate over whether these secondary spikes are real was finally put to bed when Charley Sisk at Sisk Rifles blew the end off two barrels. We have also verified changes to the rate of acceleration just prior to, and after these events. Case Closed, it is real!

[BubbaJon]

and why such new ones as LilGun and AA#9 can be made to ignite easily but burn slower than they otherwise would if they were monolithic.
Speaking of - Lil'Gun has my vote. For lack of a better term it shoots "smoother" with beeg boolits. Instead of a "Krrrack!" you get a more rounded "WHOMP". I know my groups have improved with it.

[Larry Gibson]

I never did buy off on the "barrel harmonics" reason for the secondary spikes either.

Larry Gibson

[44man]

Actually, with rifle powders the burn continues past the peak pressure point of the curve and slow powders burn quite a ways down the barrel. Maybe not all the way down and maybe not even half the way down but further than just the peak. It has been shown that a longer barrel will burn all the powder while a shorter barrel with the same loading will leave unburned kernels (that's with a specific load and powder, not any or all loads and powders). Increasing the powder charge with the specific loading will often burn all the powder. Point is some powders behave differently to others.

My uncle was an armourer in the dessert in WWII and said that after a 50 Browning machine gun shoot at the range they would sweep up heaps of partially burned powder from in front of the guns.



That secondary pressure spike has been lab tested and it's not barrel harmonics or some such. They went so far as to pack the barrel with sand bags to dampen vibration and that spike was still there.
This is correct. Powder continues to burn after peak.
If 200 gr of powder burned in the first inch of a .50 BMG, you have a BOMB.
It has been the printed word that says all is gone at peak. Attributed to gun writers. I did find that article about expansion ratio. It is false.
I talked to the powder companies and they just told me "internet idiots."
Progressive burn escapes the natural world.
Why not use dynamite? It really goes off all at once.
Maybe I am stupid but I know all powder is not consumed so fast. Smokeless is not classed as an explosive, it is a flammable. It does take barrel length to burn all of it.
Then someone said the muzzle flash from a short barrel was from the gas reaching oxygen in front of the barrel. No common sense shown because powder produces it's own oxygen or it would not work. Just maybe it is powder out there?
Someone is not thinking at all. Compare a rifle with 50,000 PSI using 35 gr of powder with a mag at 50,000 psi with double the powder charge. Did the double charge go off all at once? That would mean 100,000 PSI. Or, Heaven forbid, more distance to burn was needed.
Expansion ratio just must be more from a higher charge with the same peak pressure---RIGHT???? OH, OH, maybe you are wrong.
Put it in perspective. Why does a .50 BMG need 200 gr of powder? Just shorten the case to 1" and it will peak the same pressure and depend on expansion ratio.
Why do the guns on a destroyer need bags and bags of powder behind the projectile?
A few read gun rags for information, others think.

[Larry Gibson]

Expansion ratio just must be more from a higher charge with the same peak pressure---RIGHT???? OH, OH, maybe you are wrong.

The "expansion ratio" I was refering to is; "The ratio of the volume of the bore, measured from the base of the seated bullet to the muzzle, to the volume of the cartridge case. An expansion ratio of 9:1 means the bore volume is 9 times the case volume." (Firearms Encyclopedia).

A .38 SPL revolver with a 6" barrel actually has a greater expansion ratio than many rifles with 20" barrels. There is a maximum expansion ratio at which any given cartridge/load combination will produce maximum velocity. The .243W for example would require nearly 30" of barrel to produce an optimum expansion ratio and velocity. Many of todays "high intensity" cartridges would require barrels of 30 - 40" long to achieve the expansion ratio and efficiency of the 30-30 cartridge.

Larry Gibson

[303Guy]

By definition the expansion ratio is the ratio of the volume of the case to the base of the boolit to the total volume. Total volume is volume of case plus bore volume.

A revolver is going to have a bit of a complicated expansion ratio because one has to take into account the expansion out the cylinder to forcing cone gap.

[Doc Highwall]

Lets say for argument there is only one caliber in the world and it is a 308 Winchester with a 24” barrel, and there is only one bullet in the world a 175 grain Sierra Match king.

Now with this one combination we still have all the powders we have, and you made a powder burn rate chart from fastest to slowest at a chamber pressure of 20,000 P.S.I. and you now have a perfect list.

Now you change your mind and you want a chamber pressure of 30,000 P.S.I., your perfect 20,000 P.S.I. list now has a few changes as to burning rate.

Now do this again at chamber pressures of 40,000, 50,000, and 60,000 P.S.I. and your perfect list is again changed with each higher level of chamber pressure.

These changes are with just one gun and bullet but different chamber pressures. Think of the additional changes if we changed just the bullet weight as to the perfect burn rate chart at each pressure level.

With all the combinations of different calibers, case capacities, expansion ratios, bullet weights and bearing surface, the possibilities are endless.

Powder burning rate charts are RELATIVE AT BEST! Add to that the lot to lot variables to burning rate of +/- 10% and it can make it seem over whelming.

The secondary pressure spike is caused by not having enough moment force/ start pressure allowing not fully burning/consumed powder to follow the bullet down the barrel. As we know powder needs pressure to make it burn and with a higher pressure it burns faster. The bullet as it moves down the barrel increases the volume behind it, lowering the pressure of the expanding gases due to a larger area/volume that they now displace. Because the rate of acceleration of the bullet slows some, the not fully consumed powder catches up with the bullet and the powder now has the resistance to accelerate it’s burning speed resulting in the secondary pressure spike. As the caliber goes up the pressure drops faster for every inch the bullet moves down the barrel/bore due to bore volume. A faster powder or a heavier bullet with more bearing surface will help out, and with fillers both reducing the powder capacity within the cartridge case and helping to position it for the primer to ignite it.

[dverna]

Lets say for argument there is only one caliber in the world and it is a 308 Winchester with a 24” barrel, and there is only one bullet in the world a 175 grain Sierra Match king.
.

I could live with that selection with no issues!!!

Seriously, good explanation DH!!!

[303Guy]

What's come out of it so far is the idea to look at largest powder charge for the lowest pressure at some average velocity. That's the powder that will have a slower pressure rise with the longest burn. Look at the same powder at the starting loads to complete the assessment. Then one has to discover how well that powder lights up and burns at lower pressure. BL-C(2) appears to be ideal for cast but others have said it burns dirty at lower loadings. Varget on the other hand burns well at low levels (that's from my own observations). IMR 4007 SSC is a powder that is listed with the lowest pressures and fills the case of the Brit.

[Larry Gibson]

303Guy

The definition I quoted has been around for many years and is the understood defintion of "expansion ratio". Is it wise we rewrite and change definitions? When we do that doesn't confusion generally reign? Or shouldn't we just accept and work with the accepted definition? When we do this isn't there a consistency and continuity to the thought process and discussion over time?

The slowest powder with the highest load density is an over simplification. The powder still must ignite and burn uniformly for accuracy. Many slow burning pwders won't do that at the low end psi's for many cast bullet loads.

Larry Gibson

[303Guy]

Is it wise we rewrite and change definitions? No, not re-defining anything - Robert Boyle in 1662 and Jacques Charles in the 1800's did that. Charles was inspired by hot air balloons which were the rage at the time. Remember the gas laws?

66545

Expansion or compression ratio is defined as;

66544

(Initial volume over final volume).

Anyway Larry, you defined case volume to bore volume and perhaps that is what is spoken of in gun circles which is fine - I stand corrected (but I call it case to bore volume ratio). However, barrel lengths vary and anyway, when we are considering pressure we are really only interested in boolit sectional density. An example would be the 308 and the 243. Both cartridges would use a similar powder charge range (not too similar) yet have a very different case to bore volume ratio. They do however have a similar boolit sectional density range. So to me, bore volume is a bit of a mute point. It's the expansion rate versus case volume that I'd be interested in. That would take into account velocity (more like acceleration rate) and boolit sectional density. Not all that simple as different burn rate powders are indicated and cartridge efficiencies are different with different bore and a different case to bore volume ratio.


McGraw-Hill Science & Technology Dictionary:
expansion ratio

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Home > Library > Science > Sci-Tech Dictionary
(ik′span·shən ′rā·shō)
(fluid mechanics) For the calculation of the mass flow of a gas out of a nozzle or other expanding duct, the ratio of the nozzle exit section area to the nozzle throat area, or the ratio of final to initial volume.
(mechanical engineering) In a reciprocating piston engine, the ratio of cylinder volume with piston at bottom dead center to cylinder volume with piston at top dead center.


Read more: http://www.answers.com/topic/expansion-ratio#ixzz2PfVE6LsQ

[44man]

Expansion ratio just must be more from a higher charge with the same peak pressure---RIGHT???? OH, OH, maybe you are wrong.

The "expansion ratio" I was refering to is; "The ratio of the volume of the bore, measured from the base of the seated bullet to the muzzle, to the volume of the cartridge case. An expansion ratio of 9:1 means the bore volume is 9 times the case volume." (Firearms Encyclopedia).

A .38 SPL revolver with a 6" barrel actually has a greater expansion ratio than many rifles with 20" barrels. There is a maximum expansion ratio at which any given cartridge/load combination will produce maximum velocity. The .243W for example would require nearly 30" of barrel to produce an optimum expansion ratio and velocity. Many of todays "high intensity" cartridges would require barrels of 30 - 40" long to achieve the expansion ratio and efficiency of the 30-30 cartridge.

Larry Gibson
That is correct Larry. It is something that changes.
What I referred to was using the term to say more powder going off with a slower powder still going off in the same distance as a fast powder will add more expansion ratio without increasing pressure. It has been used to show a lot of powder just adds more gas at the start and only that gas pushes the boolit.
We know that can't be done without destroying the gun.
It is the definition of an explosion.
If it were not true, we could just double the charge of Bullseye to double the gas and so called "expansion ratio." Imagine a .50 BMG case full of Bullseye!
It started as a gun writers pipe dream and still continues today with the thought that all powder is consumed in an inch or so.
It is why some think all powder is burned in a 2" .500 S&W, you really need to fill that huge case with Bullseye. Gun parts really reach velocity that way. (DANGER)
Larry, I don't now where that thinking came from but it is still repeated.

[Doc Highwall]

By definition the expansion ratio is the ratio of the volume of the case to the base of the boolit to the total volume. Total volume is volume of case plus bore volume.

303Guy, this is my understanding of expansion ratio also.

[Larry Gibson]

303guy, Doc

The expansion ratio of gases as expressed by Boyle is correct as it relates to the total volume the gas has to expand into. However, the "expansion ratio" in reference to firearms expresses the differences in case capacities to bore capacities (volumes). That is the difference; the result means two different things. My quote was not my definition but the standard definition taken from the Firearms Encyclopedia book on definitions of firearm terms for "expansion ratio" as it relates to firearms, not to gases in general. It is also used in other books/articles discussing the subject for many years. I believe it also is the definition used by Powley for his computations as he describes "expansion ratio as "total volume inside the case plus barrel exposed to gass, divided by the case capacity.." Thus again we see as related to firearms/cartridges we have a ratio between case capacity and the total volume for the gas to expand into. A bit different from the simple total volume are of expansion as expressed in Boyles gas laws.

That being as it may we are essentially saying the same thing. Earlier I posted "The exact bottom end of that level is very dependent on the exapnsion ratio, bullet weight and case volume (load density).". Your use of "sectional density" equates to "bullet weight" as bullets of equal SD in .30 and .243 caliber are comparatively the same in relation to the expansion ration of the .308W vs the .243. Same thing just different terms.....still the same page of the hymm book.....as it relates to your original question.

Powley also states that for a good working pressure the only 2 factors involved are the expansion ratio and the powder charge to bullet weight. That is what we are basically discussing except that at the lower psi's of cast bullet loads the psi level at which the powder itself will ignite and burn efficiently also must be considered. That is important because regardless of "burn rate" every powder has it's own psi level based on composition and retardent used for efficient ignition and burn.

Larry Gibson

[RobS]

Varget on the other hand burns well at low levels (that's from my own observations).

Yes, my observations parallels yours in that Varget burns well and it does better than IMR 4064 for me; Varget is also more consistent throughout the year as ambient temperatures change. I thought about trying H4895 but chose to stay with Varget to have a bit slower powder to fill the case more.

[Larry Gibson]

44man

Another quote from Powley if I may which adds to your premiss; "a gun with low Expansion Ratio and a high ratio of Powder Charge to Bullet Weight will be affected much more by barrel shortening than will a gun of both high Expansion Ratio and low atio of Powder Charge to Bullet Weight.

Larry Gibson

[BAGTIC]

The reason the high expansion ratio example is less effected by barrel shortening is that by the time the bullet reaches the end of a long barrel it has already run out of steam, so to speak. If the muzzle pressure is only 5000 psi less performance will be lost than if it is 15000 psi. The low charge/high expansion example will be more efficient but not necessarily more effective than a round with high charge/projectile ratio. A lot of shooters are less concerned by efficiency than by effect. They are willing to burn a lot more powder in exchange for a modest increase in performance.

[44man]

44man

Another quote from Powley if I may which adds to your premiss; "a gun with low Expansion Ratio and a high ratio of Powder Charge to Bullet Weight will be affected much more by barrel shortening than will a gun of both high Expansion Ratio and low atio of Powder Charge to Bullet Weight.

Larry Gibson
Exactly.
I read a lot of powley long ago but confess to forgetting so much at my age.
You and Doc make sense.
Common sense says powder burn rates are made for a reason. Size of grains, holes in the center, deterrents to slow ignition and burn speed, shape of grains, etc. Many powders are the exact same formulation but just changing shapes and coatings will change the burn rate.
What is burn rate? It sure does not mean all powders go off in an inch. It is control.
So many think it is all gone quick so look at the space shuttle. It does not get a huge blast at launch and go out. The propellent burns most of the way to orbit.
Compare the old Bazooka with a rocket.
The boolit is really a rocket, prolonged push until it leaves the bore. Bore length can extend or shorten push.

[BAGTIC]

Increasing the powder charge does not increase the expansion ratio. It reduces it. To increase the expansion ratio one increases barrel length or decreases chamber volume.

[Doc Highwall]

No matter what way we look at it there is a point of no return with expansion ratio, some times called over bore, but what about being under bore?
A 22Lr. with a 28" barrel like on a Winchester 52 certainly does not have enough powder gasses to burn the whole length of the barrel to provide a constant rate of acceleration. At some point the powder has been completely consumed, but the gases are still expanding, but at a slower rate until they reach zero pressure. In the case of the 22Lr. in a 28” barrel the bullet could even be de-accelerating due to bore friction in the last couple of inches of the barrel. This should help to make more uniform the gas pressure as the bullet is released from the muzzle.

Unfortunately the longer barrel adds more barrel whip/nodes that can cause a greater dispersion of the bullets on the target, A chronograph could even show that this is a good load with low standard deviations and extreme spreads. (A good thing for barrel turners.)

Barrel volume in cubic inches for a 20” barrel.
.223 = 0.75 .243 = 0.90
.257 = 1.00 .264 = 1.06
.277 = 1.17 .284 = 1.23
.308 = 1.45 .312 = 1.49
.323 = 1.60 .338 = 1.75
.348 = 1.86 .358 = 1.97
.376 = 2.17 .458 = 3.24

Basic math: For a enclosed bore, the volume is proportional to the square of the radius,
If we double the bore diameter, the bore volume increases 4 times.

With the above chart it shows that a larger caliber with a smaller case capacity can be more efficient with a shorter barrel.

[44man]

Now we are getting somewhere.
Yes a .22 runs out at something like 16" but a longer barrel can still make it more accurate.
Don't depend on me for math!
To make shorter barrels for larger and larger calibers and brass just does not work good.
Yes, I get a 45-70 to shoot in a 10" barrel but it is with one powder and never a case full to utilize the capacity. It is just the gun and twist that makes it work. It will never be a rifle. I knew I had a handful because even a 30-30 in a 10" barrel is nuts.
A larger case reduces pressures, that is true and I can make the 45-70 shoot as fast as a .454 with less pressure but will never reach what a long barrel can do.
Too many believe a 10' fireball out front makes the gun more powerful. The recoil from a short gun MUST make the gun more powerful!
Too much powder adds to projectile weight and that can reduce velocity. That is because the powder is not all gone in an inch, it is being pushed down the bore. Peak is higher from more weight but the powder can not all burn so much is ejected.

[303Guy]

Yup, we're all on the same page - great inputs, thanks.

Just a thought coming from the powder adding to projectile weight - it increases recoil! Mmm .... it may be true that the fire-ball does not mean more power but it sure does mean more fun! :mrgreen: In the world of suppressors that higher mass and higher pressure muzzle ejecta is good for reducing recoil. Without suppressors it's bad for muzzle the unprotected ears.

I've found load data for H4350 that indicates it does burn OK at lower pressure and I have loaded it quite low - as low as 65% case volume but with filler under a 147gr boolit.

Anyway, something I'm surprised at is the muzzle velocity attained by my 15½ inch barrelled 303 Brit pig gun. A 194gr boolit doing 2000fps using a case full of H4350. I'm still interested in increasing the bore of that gun for the purpose of getting more power out of its short barrel. Not more than 2000fps but a heavier boolit - maybe slower though. I don't really see the need to drive a heavy boolit above 1800-1900 fps other than to gain a little more 'reach' i.e. extending the point blanc range. Another perceived benefit is lower muzzle pressure which I see as a boolit de-stabling factor. Has anyone found a difference in accuracy with lower muzzle pressure versus higher muzzle pressure?

[303Guy]

So I put on my hearing and eye protection and tried a load of 30gr W780 with only Dacron filler (1gr) under a 206gr paper patch boolit and hoped. That's 60% load density. Well, just a soft thump was all there was. Boolit expansion was 530% and penetration into the media was 12 inches/300mm and weight retention was 100%.The primer shows a little more pressure than a no powder load i.e. not much to see. But there was some base edge feathering on one side - not good! Obviously with paper patching there was zero rifling skid. So the powder looks promising but the alloy looks too soft but OK for that velocity (I wish I knew what it was doing). I'm going to repeat it with a plain cast boolit which is lighter at 192grs. For the paper patchers, the patch came off in long strips.

[303Guy]

Right. I repeated the test with the same boolit weight and stronger alloy and got less expansion but a similar expanded diameter but greater penetration into rubber grounds. I also did the plain cast test with a lighter boolit of 192gr and this time there was unburned powder kernels. Even so, penetration and expansion was about the same. So it seems the lower limit for W780 in the 303 case is 30grs under a 206gr boolit. One can hardly tell from the primer that the case had any powder in it. The next step is to load up a few rounds and go test them and chronograph them. That could be a while.

[44man]

Some things work extremely well. My MOA in 7BR has a 10" barrel and would just scatter the 120 gr bullets until I tried Varget. I want the 120 gr for deer. I got it to go 2175 fps with 32.5 gr and it does 1/2" at 50 yards. It burns very clean.
I use 4759 with a 154 gr but go to H322 for 162 and 175 gr bullets. The 175 gr load is max but will poke one hole at 100 for 5 shots. 1898 fps.
Someday I will try Varget with the heavy bullets but there is no load info for it at all because it is not supposed to work.
The little case is very efficient.
Back when I had a 30-30 with a 10", only 4759 worked right, back to one powder like the 45-70. A 12" to 15" barrel would be so much easier to work, the large cases are just not right in short barrels.
To hear of guys buying a 45-70 or .500 S&W with 4" barrels will give them too much to chew on.
303, good to hear some of the powders you use can be reduced. That is the hardest thing to find. That scares me more then a little over max with some powders.
The next thing we did was to use much more Pyrodex and compress it more to fit a 45-70 BPCR. That was the funniest thing ever, we had plugs of Pyrodex fly out the muzzle like flares to burn in the grass. Then we increased the charge of BP and once a certain point was reached, velocity started to drop and never stopped dropping as we added more powder. Recoil increased a lot. A 34" barrel could not burn it all.
I don't think muzzle pressure has too much affect on accuracy if the crown and boolit bases are perfect. It is just wasted powder.
Looking at the .22 with a long barrel where the bullet is slowing might just mean the bullet used does not want to be too fast or over spun.

[Doc Highwall]

I think if you look at the chart I posted in post #44, you can see how fast the bore volume can jump like comparing
.308 = 1.45 to .458 = 3.24, the volume is more then twice meaning the pressure will be less then half with the same powder.

[Doc Highwall]

I think if you look at the chart I posted in post #44, you can see how fast the bore volume can jump like comparing
.308 = 1.45 to .458 = 3.24, the volume is more then twice meaning the pressure will be less then half with the same powder.

[44man]

I think if you look at the chart I posted in post #44, you can see how fast the bore volume can jump like comparing
.308 = 1.45 to .458 = 3.24, the volume is more then twice meaning the pressure will be less then half with the same powder.
Hey, you got a double post! :lol:
Yes, very true about volume.
I get funny thoughts like a .500 S&W with no barrel, just the cylinder or a single shot with such a short barrel the boolit is sticking out the muzzle. Fill the case with powder. There is a high giggle factor. Yet a few think a 2" .500 S&W is the ideal back up gun.
I don't know Doc, how is it ever explained?
According to gun writers the powder will all be burned in the case since it is longer then 1". We need to have rifled brass. :kidding:

[subsonic]

I think it depends on what you mean by "burned".

Obviously if you are finding unburnt powder in the case or on the ground, something is wrong and it could be that the pressure drops in the barrel before all the powder has a chance to burn. Smokeless requires pressure to burn quickly, as anyone that has lit a pile of it and black powder can attest. The black will flash, but the smokeless will just burn and smolder.

If you can hold the powder back for longer with a heavy boolit and lots of friction from the bore or case, things will improve.

There is a point where you can still gain, eventhough it is not very efficient. Your 2" .500S&W would be a good example. Lots of unburned powder, but I guarantee that if you slide a .500JRH loaded with a max charge and the same boolit in the cylinder and touch it off it will still be slower than the .500 S&W with a max charge and the same boolit. Now, maybe not a lot, but some. And it will have taken a bunch more powder to get it done too.

It's all relative.

I have a .480 Alaskan on order that I think might shed some light on this once it meets a reamer.

[44man]

No, I don't think the JRH will be slower and might be a lot faster.
The thing to look at is the much larger powder charge in the S&W adding to boolit weight and raising the pressure. Less efficient use of the powder with more blown from the muzzle and more cost.
How about a case half the size of the JRH? Would it be slower in a 2" barrel?
I can't answer it. I have nothing to work with.
The point of diminishing return changes with each cartridge and a whole lot higher load can mean 20 to 50 fps gain, some might reach 100 fps or more but the cost of pressure and money negates it. These are velocity advances not needed for any reason.
Another thing not looked at is the accuracy, velocity position. A boolit needs so and so velocity and spin so if you shorten the barrel and reduce the velocity, you start to make a lot of noise only. It might be only 50 fps to turn a golden load to a scud.
Now you need to raise the pressure in the short barrel to gain the 50 fps but find it can't be done. Now you change to a faster powder so the case capacity is of no use.
All is give and take.
It amuses me when someone uses Unique, 2400 or a faster powder in a 45-70. What is the huge case used for and why not a .45 Colt?
I have two theories not to be confused with anything of course, just my ideas.
A short barrel is better with a smaller case and a short barrel should have a faster twist rate.
There, I let the Genie out of the bottle!

[303Guy]

Interesting thing about 'unburned' powder is that it has changed colour so I'de assume some degree of gas release has occurred and obviously some of the powder has burned but why does the flame go out? Makes me wonder about those secondary pressure spikes on pressure traces. Do those partially burned kernels suddenly detonate - if there's enough of them and the barrel is long enough? Why do I not find them when the boolit is a little heavier? Do they simply continue burning outside the barrel after some point. There didn't seem to be much difference in velocity.

Then I start to wonder whether there is any point in going so low in charge even if the velocity is where I want it to be when I can achieve the same thing with a faster powder like W748. I'm aiming for a gentle launch and a high muzzle velocity with most of the velocity gain taking place further down the barrel. At the end of the day only accuracy with decent velocity matters. I found it interesting that H4350 could drive a fairly heavy boolit that fast in so short a barrel. I should chrono that load in a longer barrel.

Something I haven't done yet is burn some powder in a pan to see what the residue looks like and to compare open burn rates.

[44man]

303, powders are just so different. Some need pressure, some just a fire. Some will be scorched and not light.
A powder that changes color only means the coating was not broken through to reach the powder. It could be heat or pressure reduction but I will blame heat loss.
You will not find much burning powder in a pan. The only thing you will see is some powder needs fire held longer until they light. It is the coating that retards flame.
Even BP has a carbon coating so you need to hold a match on it for a time but then it all goes.

[subsonic]

Powders are definitely different and using them "off the map" may give some interesting results that don't follow the rules.

Gather up some o those "unburnt" kernels and see if you can get them to light with a match.

[44man]

Powders are definitely different and using them "off the map" may give some interesting results that don't follow the rules.

Gather up some o those "unburnt" kernels and see if you can get them to light with a match.
Yes, they burn very nicely. They light faster then new powder too.

[303Guy]

Curious that they should light easier yet went out in the barrel when things were much hotter. Not enough oxygen under the conditions maybe? Mind you, enough oxygen will burn anything. Almost.

[303Guy]

So I burned five powders open. Not much to learn really but they all burned completely. Shotgun powder burned cleanest but while they all burned differently with different flame appearance and slight lighting differences most left a dark ash but no partially burned kernels.

[uscra112]

Curious that they should light easier yet went out in the barrel when things were much hotter. Not enough oxygen under the conditions maybe? Mind you, enough oxygen will burn anything. Almost.

In gunpowder, the oxygen is in the powder.

[44man]

Powder makes it's own oxygen so none is needed in the bore.
Ever see the oxygen canisters in airplane ceilings? It uses a material that is ignited and gets hotter then blazes to generate oxygen.
As to why kernels don't burn in the barrel is a mystery. Either they are driven ahead of pressure and out of flame or it is the dropping pressure. I have see too much left in brass though for that to be an answer. 3031 did that in the BFR 45-70. Yet the same load did well in a rifle. Is time a factor? What does primer pressure do?
I would love to have a primer with a lot of fire and very little pressure to play with. Not the nature of the compound though with most primers having 2000 psi by themselves. The standard primer has almost as much pressure as a mag but I do see a difference with every single caliber change, larger needing the mag. I get the .454, .475 and even the JRH to light off with a standard LP primer but accuracy improves a lot with a mag. The opposite with the .44. If you say it is only cup thickness, I will say you are wrong, there is too much difference. Does the mag have a little more compound or is the formulation different?
What affect does a primer have when you have unburned powder?
I use a LP mag primer in the BPCR, 45-70 and put a disk of newspaper over the flash hole to keep powder out of the flash hole. The paper turns black but does not burn, some I pick out are still paper and you can read the print. I have never found the paper missing. The heat happens too fast and is gone fast. The primer just cuts a hole in the center.
I also find Dacron on the range that has not melted. Wads under a boolit can be used again.
To think there is a huge firestorm is wrong, the brass and barrel steel sucks the heat up.
No math involved here from me! [smilie=s:

[303Guy]

In gunpowder, the oxygen is in the powder.
Yes, but only so much. Enough for a stoichiometric burn or enough for a rich burn or enough for excess oxygen? Excess oxygen burns fuel faster and hotter. What I was thinking is that in air, there is all the oxygen in the world for complete combustion while inside the barrel there is only enough and that in the violent conditions in the bore the flame may go out when the pressure suddenly drops. By violent I mean things are moving around rapidly (plus all the other bits). One way of slowing a powder burn rate would be to provide less oxygen for a full burn i.e. a reducing flame. In a reducing flame there is a lot of CO produced and some CO2. All the H2 is burned regardless. In an excess oxygen flame all the CO is consumed to form CO2. In a stoichiometric flame most of the CO is consumed to form CO2. But in a barrel under flame induced pressure, the heat is required to release the oxygen so maybe at the point of pressure release, the temperature drops sufficiently to halt oxygen release and because of the motion of powder kernels combustion ceases. I'm not sure what fuels powder contains but I'm guessing it's not just carbon and hydrogen - that's what BP uses with some sulphur as a combustion accelerator. By the way, enough heat prevents CO from forming CO2 and actually causes CO2 to dissociate to form CO + O2 which then recombines as the temperature falls to release more heat.

On the use of pistol powders in large cases, it makes sense for low velocity loads because those powders burn well and fast. The large case serves to absorb the gases produced, thus keeping pressure low but developing quickly and the larger the case the more gas can be contained which maintains the pressure longer as the boolit recedes down the bore.

[Larry Gibson]

If memory serves me correct this subject has been discussed for years. Regardless of the continual discussions smokeless powders and BP have sufficient oxidizers in them. The small amount of oxygen that may be still in the case is of no measureable consequence. Hence in load development it is never a consideration.

I am intrigued by your thesis of "But in a barrel under flame induced pressure, the heat is required to release the oxygen so maybe at the point of pressure release, the temperature drops sufficiently to halt oxygen release and because of the motion of powder kernels combustion ceases.". This may well explain why we get unburned kernels in cases of low expansion ration with some powders such as 3031/4895 in the 45/70(?) until a certain level of psi is reached.

Larry Gibson

[44man]

You bring up something of interest. Too much CO2 or other gases that damp flame.
Now think a little. There is no free oxygen behind a boolit and no way for it to get in. There is a little in front of the powder charge but it is a sniff. From ignition to boolit release, there is NO additional oxygen except what powder produces. Even a grain of powder ignited makes oxygen. Nothing on earth burns without oxygen. The three things, fuel, oxygen and heat. Take away one and the fire goes out. Take away heat so powder can't make oxygen and you lost two for fire. Fuel alone does nothing by itself.
Pressure is funny and you can cut steel with water pressure but it does not melt steel, it will not start a fire.
When you pressure wash your deck, does it burn the wood?
You turn gas into liquid with pressure and it is COLD, like propane or liquid nitrogen, CO2 is cold or made into dry ice.
Compress air and the machine gets hot but the air is cold. Does pressure in a gun make powder burn? I would say the heat is like what a compressor makes at the piston that is doing work. Fill your compressor with high pressure air and feel the tank, will it start a fire?
LOX is VERY cold.
So does pressure in the gun actually remove heat? Is the high pressure what saves the gun from burning up?
I am out of my element here. But an explanation of how pressure makes stuff burn faster unless you compress oxygen, release it to make stuff burn needs to be explained to my stupid brain. The fuel still needs heat even if sprayed with LOX.
Oxygen will create heat through a nozzle when released and oil in an oxygen hose fitting will ignite. Out in the open, oxygen will not light oil without a heat source.
The triangle can not be broken.

[303Guy]

44man, you are by no means stupid. Heat and pressure are pretty much the same thing. Heat is the kinetic energy of molecules and pressure momentum energy - pressure is caused by molecules impacting on a boundary, in this case the chamber, bore and bullet base. The heat of compression in a comressor may not seem like much but remember that the pressure in a cartridge is a great deal higher, in the order of brazillion psi's. You will burn your hand on a compressore outlet at only 150 psi. A diesel engine will ignite its fuel just on the heat of compression. That's a cold engine (in the old days - my days - a heater coil was required to start a cold diesel engine).

[madsenshooter]

303 guy, you mentioned IMR4007SSC previously. I just used the 43gr start load Hodgdon has for the .303 w/174gr j-word in a Krag with a 168gr cast bullet the other day. It burned well, pressure should have been relatively low, velocity 2300fps or so. The burn was fairly clean and accuracy wasn't too bad considering the velocity with a not too hard alloy. Others have said it burns dirty when you get down to cast pressures, but maybe they went down too far. It was cleaner burning than an equal charge of H414.

[303Guy]

Sounds good. It's available in my parts I see. Thanks, madsenshooter.

[44man]

44man, you are by no means stupid. Heat and pressure are pretty much the same thing. Heat is the kinetic energy of molecules and pressure momentum energy - pressure is caused by molecules impacting on a boundary, in this case the chamber, bore and bullet base. The heat of compression in a comressor may not seem like much but remember that the pressure in a cartridge is a great deal higher, in the order of brazillion psi's. You will burn your hand on a compressore outlet at only 150 psi. A diesel engine will ignite its fuel just on the heat of compression. That's a cold engine (in the old days - my days - a heater coil was required to start a cold diesel engine).
For sure, compression does make a lot of heat and a compressor gets very hot like a diesel but once the air is out of the cylinder, it loses heat. If you spray fuel into the cylinder it will burn but you can not burn any if you spray it in the storage tank.
So what happens to powder as the boolit moves and pressure is dropping?
There might be something in what you say about grains bouncing all around and getting out of the flame. The fuel is no longer contained.
Some powder can be ignited with impact like pounding out a stuck round from a chamber. That is like a piston.
It gets harder---why will a powder not all burn in a short barrel so you have powder grains in the brass, bore and on the bench but it will all burn in a longer barrel? The pressure peak will be at about the same position and I can not figure what happens AFTER peak.
Could time be a factor? Is time needed to erode the coating? Do grains of powder get slammed together hard enough to break the coating?
I think about a catalytic converter where the platinum gets so hot it burns and alters all the gasses going through it. Why doesn't it melt the whole thing off the car?
Is there a chemical reaction we miss?

[303Guy]

I'm not aware of the platinum getting so hot. I suppose it does considering hot gasses are undergoing further combustion in contact with it.But it's the platinum causing the reaction, not just the heat. I think it is the time that makes a difference between a short barrel and a long barrel. The time required would be altered by raising the pressure and temperature with a heavier bullet or more powder.

Just to clarify what pressure is; it's the total momentum of the gas and 'dust' impacting the container walls on a specific area, so a large number of molecules or dust particles at a lower momentum per molecule or particle would exert the same force as fewer particles or molecules with higher momentum. That's were temperature comes in. What temperature does is dictate the force of impact of the molecules against each other which is what causes chemical reactions - the high velocity impact of molecules which force say oxygen and carbon molecules or atoms close enough together to bond together forming CO2 (oxygen exists as O2).

So I'm suggesting that as the projectile leaves the barrel the burning gasses rapidly vent out the muzzle, resulting in fewer high velocity impacts of molecules on burning kernels so they flame out. You see, although the molecules and kernels still have the same kinetic energy as before, they all move in the same direction and so don't impact each other any more. Well, not quite so simple as that.

[44man]

Too bad it can't be watched in ultra slow mo. Need a see through gun! :veryconfu

[popper]

Just don't understand the quality of burn and pressure thing. Unless it's a chemical reaction rate that depends on pressure.

[runfiverun]

don't forget about the surface area of the powder.



ohhh yeah, and I doubt anybody uses platinum in a cat any more, they use lot's of other stuff now like palladium.

[303Guy]

Just don't understand the quality of burn and pressure thing. Unless it's a chemical reaction rate that depends on pressure.
That's what I understand it to be, heat and pressure. But if one burns powder in air, I think something quite different happens. For a start there is plenty of time and the kernels stay together while they burn (and it's fun to watch). I've never tried a set up with some of the powder covered by something like sand.

An analogy to try to understand heat and pressure and chemical reaction caused by it is to think of a shotgun loaded with steel shot. Actually, make that ball bearings. Anyway, if those are fired at a hard steel plate, there will be no collisions of the steel balls until they hit the steel plate and bounce back. Then a few will collide with a few of those still incoming. Now that plate will feel the effect of the multiple hits as pressure and it will act like the sides of a gas container for a few milliseconds.

In a jet engine, two things are required to burn the air-fuel, firstly compression and secondly something to hold the flame retainer which also hold the fuel spray nozzles.

Talking about unburned powder and those unburned kernels that light up easily, maybe this is what causes the mysterious SEE. Ignition occurs, the projectile moves forward down the bore dropping chamber pressure below that required to maintain a steady and progressive burn and the projectile slows (or maybe even stops) then the burn build up pressure and burns faster, too fast for the projectile speed to create more volume so the pressure runs away and we have a Ka-Boom! It all seems to make sense to me now.

[Doc Highwall]

The powder burn rate is very much influenced by the pressure! With more pressure the faster it burns and with less pressure the slower it burns.

The longer the length of time that the powder is subjected to a higher pressure the more completely it burns. This would be correctly called the “Time Pressure Curve”. An example would be a 30-30 Winchester and a 22-250, load them with the same powder and bullets of approximately the same sectional density, a 80 gr. 22 Cal. @ .228 and a 30 Cal. 150 gr. @ .226. The barrel volume in cubic inches for a 24” barrel in 22 cal. is 0.90 and a 30 cal. is 1.74, the 30 cal. has 0.84 more cubic inches of bore volume then the 22 cal. or 93% more volume.

Because of the greater volume in the 30 caliber barrel, the “Time Pressure Curve” will drop at a much faster rate then the 22 caliber barrel directly affecting the combustion of the powder, leaving un-burnt powder in the barrel with a lower muzzle pressure at bullet exit.

[popper]

The powder burn rate is very much influenced by the pressure! With more pressure the faster it burns and with less pressure the slower it burns. My SWAG on this is that the chemical reaction is different at different pressures, not the fuel/air ratio. Detroit reduced compression ratio to reduce NO byproducts. It fits with the low pressure ignition theory. My thought is the primer has to create the pressure (and heat of course) to create the proper reaction that burns fast. Some powder lights off and keeps the pressure up. Powder that doesn't 'light off' goes out the bbl or is left IN the bbl. as determined by bbl length and burn rate. This would also explain the position sensitivity and somewhat the S.E.E effect. My guess is Boyle's law and expansion ratio just determine velocity.

[44man]

Understood pressure is needed.
When I remove a fired case and pour out powder, just why didn't it burn when it is behind the peak and subject to all the pressure?
There is just too close a relationship between pressure and fire. It would appear not enough fire does not aid the pressure work.
How much pressure is needed? Looking at loads that run at 14,000 cup all the way to 60,000 psi, it is only the powder type and it's burning speed and how flame propagates.
Gas can create huge heat when released fast as when it leaks past a boolit or out of a nozzle but most in he gun is kind of bottled up and the boolit base doesn't melt. You can get powder kernels impacting the boolit and making dents.
You can make an airgun diesel with oil but I don't think powder will diesel.

[felix]

Yeah, powder will diesel, Jim! Call it a SEE condition, if you and Larry will bend the rules a little. The ratio of air, heat, pressure is regulated for the powder designation. The "engineering" applications of shape, surface type, and porosity of the kernels is all in cahoots with the chemical deterrents to make up the "required" powder "speed" per cartridge. Ignition of the latter day smokeless powder design relies mostly upon the primer's wave production to overcome the various deterrent formulations. Also, additional air outside of the muzzle will make some powders act like a flame thrower. These powders are typically composed with heavy deterrents to maintain a low and LONG pressure curve intentionally for recoil reasons. These powders are typically triple based to keep pressure up to snuff throughout a long barrel (or a wide one). ... felix

[303Guy]

Triple based? Interesting, please tell us more. In fact anything on what makes up makes up a powder is interesting.

Something about unburned powder I remembered from a discussion on muzzle blast suppressing firing tubes - the ones set up on ranges at the bench to shoot through. In particular, we were talking of a tube made up of car tyres. Apparently black powder can deposit enough unburned powder in the tube (or box) to ignite with a boom! I'm not sure if I can understand how BP doesn't burn completely outside of the barrel.

Powder dieseling? That's a thought. Dieseling is ignition by heat of compression. The airgun dieseling is the perfect example of this. (It works best by squirting oil into the cylinder chamber and firing a shot before setting it up for the dieseling. That produces an oil 'smoke' in the bore just ripe for ignition. I have speculated that an oily chamber could cause dieseling behind the bullet by the pressure in the case injecting trapped oil into the throat. Whether there would be enough oxygen to burn it at that point, I don't know. There is air in the case and who know's whether more oxygen is released early to create an excess oxygen condition required but is so, it would unnaturally raise the pressure too early for the particular load. Plus it would be inconsistent from shot to shot so could upset accuracy that way. It may sound a little fanciful but I routinely lube my loaded rounds (not with oil - with case lube) and they come out the dryer after firing so there is a lot happening in there.

I'm going to test the same powder and charge in my short barrel gun next. I know H4350 burned clean at quite low charges (60% load density) in its 15½ inch barrel.


don't forget about the surface area of the powder.

H4350 looks identical to Varget the only difference being the kernel diameter. That would reduce the overall surface area (each kernel has a larger surface area).

[popper]

Nitro glycerin & nitro cellulose (TNT) are pressure sensitive and the primary components in smokeless powder. One could say dynamite doesn't need pressure, it actually creates it's own cause it 'burns' so fast. Kernel shape, surface area, retardants all control how much of the kernel can get burned at that instant, so yes they do control the 'burn rate'.
NO is a wasted byproduct but NO2 releases oxygen to carbon when pressure gets high enough. Powder in the case is the same as powder in the bbl. Doesn't get consumed and gets left behind, although I've never seen it. I have seen left over in the bbl, from heavy loads.

[44man]

This might be one of the greatest discussions ever! But will we ever know? Still, just talking about it as so interesting. I hope it continues but I am starting to lose ideas.
To just see everyone come together has been great.

[runfiverun]

this is gonna be linked to my something that may help sticky so it doesn't get lost in time.
hopefully the discussion keeps on going.

[303Guy]

I found unburned kernels in the barrel, case and on the catch rag.

Well, I did that test with covering some powder with sand with some exposed. It ignited just fine and burned slowly with a nice flame then died down and fizzled in the covered bits releasing heaps of smoke. I think what we see when we burn powder in air is just that - powder burning in air, using oxygen from the air. So, confined powder fizzles for a while, producing combustible vapour or smoke which will take of in a big way when the oxygen level gets high enough and the temperature and pressure gets high enough which should be pretty quick but not quite instantaneous. A SEE is beginning to look like no mystery. If that powder fizzles and produces a combustible mixture while the bullet isn't moving fast enough it could suddenly catch and burn too rapidly for the bullet to accelerate and explode. I have seen a powder doing a fizz-bang thing in a Martini Henry. That was just a 'undeveloped' SEE. And every shot did it. I'd say with the right load one could produce a SEE with every shot (and gun - one SEE per gun:violin:).

Anyway, I'm about out of speculations and now need some facts or proof or at least strong indications. Are there any combustion chemist out there to inform us?

[Doc Highwall]

Check out this page just over half way down and look at the pressure spike.

http://shootingsoftware.com/

[303Guy]

Yup. That's the one. They are not all that severe and are sometimes right close to bullet exit. I'm planing on attaching a load cell to my barrel and connecting it to a recorder for play back through my PC. I won't be able to measure pressure but a line on a graph is what I can get with no values.

[44man]

Check out this page just over half way down and look at the pressure spike.

http://shootingsoftware.com/
That knocked me off my seat----120,000 psi? Why from a worn barrel?
(There are simply too many variables unique to each firearm and a "theoretical" peak pressure has little value for optimizing loads.) This is the truth.
I never got quick load to load on my computer and it might be good for some stuff. A friend is using it to go crazy with a revolver, he scares me. I just don't know if I would trust the program.

[popper]

303guy - load cell or strain gauge? I saw they had a BT gauge setup, don't know how well that would work. Biggest problem is calibration. I suppose one could use a hot factory load to get max and go from there. Larry G ran some of my loads through his rig, confirmed they were giving a double report, 2nd was at the exit. Every once in a while I use the Powley computer to ball park some loads. Unfortunately they don't have many powder selections.

[303Guy]

Brain hickup! Strain gauge is what I meant. No chance of my calibrating it and I don't need to. It's the shape of the trace that matters and simultaneously measuring the muzzle velocity would give an indication of the mean pressure which can be used to give a value to the x-axis and y-axis. I'd be more interested in the y-axis, that being the time axis as I could then see where in the barrel peak pressure occurs and the pressure rise rate in the throat area. The idea is to see how different powders and different loads behave. Powder burn consistency would be observable too which I consider very important.

I once played with two powders in a 303. I plotted powder charge against velocity and found that one powder produced a gentle curve which could be fitted to an equation while the other powder produced a curve that went ballistic as I increased the charge with velocity increases out of proportion the the powder increments. From that I saw the danger of an overload with that particular powder and also the sensitivity of small powder variations at higher end loads. The first power on the other hand was wonderful stuff with consistent velocity increases with powder increments, indicating relatively low sensitivity to to small powder variations. Indeed, that powder produced shot to shot variations of 3 to 6 fps in two guns, my mini-14 and my 303 Brit. In fact, the velocity spread could be attributed to the accuracy of my chronograph which had a resolution of 1 m/s (3 fps). It was an accurate powder at the target too. I could hit a beer can (empty) at 200 meters!

Why would a worn bore produce such a massive pressure spike? One can only speculate but I wonder whether it has something to do with lack of bore resistance allowing the expansion rate to be too great to build up enough pressure earlier in the bore. I see that result as being of high significance. I would have been great if those guys had increased the powder charge to see how that spike would have responded. It might have disappeared or gotten much worse.

[Larry Gibson]

Strain gauges are already "calibrated" when you buy them. I don't know about the software used in pressure spike site but with the Oehler M43 the "calibration" data is input into the program. Additionally Dr. Oehler recommends the use of factory ammuntion as a "reference". Unfortunely many confuse the use of "reference ammunition" with calibration. I was fortunate when contacting Federal and Winchester to get the psi data (transducer) and conditions for several lots of factory ammunition from each that I had. With that it was very easy to see when testing that factory ammuntion the M43 was quite accurate. Factory "reference ammuntion" (a lot of factory produced ammuntion that demonstrates quite uniform internal ballistics that is then set aside for use as "reference ammunition") is very expensive and hard to obtain.

I also test as many different factory and milsurp (if available) cartridges for each cartridge I test. This gives a baseline to compare the handloads with both velocity and pressure wise. Additional I have a large lot of M118SB that I use as "reference ammunition". Each time I set up the M43 a test string of 7 shots is fired with that rifle and the same test rifle. If the results are not within the varience of different test strings and condition variations then I know something isn't correct and it is corrected before the test is run.

BTW many mistakenly believe that every factory cartridge is loaded to the SAAMI psi MAP level; such is definately not the case. Very few factory cartridges, even after calculating the "reference" offset, are at the SAAMI MAP. The psi of most factory cartridges in commercial chambers is considerably below the SAAMI MAP for the cartridge. Factorys leave a fudge factor (for good reason) in the psi level.

Larry Gibson

[Doc Highwall]

Larry, the strain gages that come with the RSI unit have a gage calibration factor to input into the program.

[44man]

Can I get crazy? How about a row of strain gauges from the chamber to the muzzle to read the whole pressure trace.
One LU or CU or strain gauge reads pressure at one spot and peak can be before or after it's position.
The slope away from peak can not be read over distance. You only see what the strain gauge sees at it's position.
You will see strange stuff with a strain gauge when pressure returns to give a spike. This will not be seen with CUP. CUP is static as is LUP. The lead or copper crush positions are not changed with powder types that change peak distances. They ONLY read chamber pressure at where the crusher is positioned.
How much different is a strain gauge position? Is it at peak, before or after?
Since each powder is different, should not the strain gauge be in a different position.
We need a long gauge from chamber to muzzle.

[felix]

Like the dictionary definition of SEE, the dictionary definition of expansion ratio means nothing to us as well. Reason: the definition does not include the function of TIME! We, on this board, are interested in dynamic definitions, not static definitions. In other words, the rate of change of something is paramount to our definitions, questions and answers. In other words, being late to this thread, I need to know what the various premises are before I can respond with my proverbial short answers. ... felix

[Doc Highwall]

44man, the strain gage is attached over the middle of the chamber. The outside of the barrel dimension along with the outside of the cartridge/inside of the chamber dimension is input to within .001" so the actual wall thickness where the strain gage is attached, and finally the case wall thickness is input for that barrel.

Because the strain gage is attached over the center of the cartridge and the known thickness of both the steel barrel and brass cartridge are known the strain gage can read real pressure in real time. As soon as the primer fires the strain gage starts to record pressure and will continue until the bullet exits the muzzle.

Click on the web site I posted above and look at the traces, you will see that with chronograph input of muzzle velocities that it will show where the bullet exits the muzzle.

[303Guy]

But is is possible for the pressure to be different at different positions in the bore? That's not too crazy if one has a look at gas laws as pertaining to gas flow through a nozzle. is that pressure spike being caused by a gas pressure wave rather than detonation of a combustible mix of gasses made up mostly of burned gases? One must ask where the energy is coming from to generate that pressure spike.

My idea with the strain gauge is to simply plot current against time and obtain a curve. If I can compare that to a factory cartridge to give some vague pressure meaning to the curve then fine but for me it's going to be about the shape of the curve, not the actual pressure producing it. Knowing the velocity will give some meaning to the area under the curve but that's about it.

[Doc Highwall]

303guy, look at my post #84 and go to the web site and save it under your favorites. If you read all the way through it you will see it gives other sites as reference to what can be done with this equipment.

I was sold on it and when I had my money saved I purchased it and now I am a happy camper. It will open new doors as to your understanding of internal ballistics.

What I thought I knew, I now know differently with a much better understanding.

[303Guy]

Thanks, Doc Highwall. I do have that one saved to my favourites. It will be sometime before I can lay out the cash for one of those but I do agree that it is the way to go. But until then I want to connect a strain gauge to my PC via a USB oscilloscope adaptor. One can view a trace using an audio oscilloscope software package such as Nero.

What I need too is a means of chronographing inside my test tube. I do have some ideas that will utilize my Chrony.

[popper]

The strain gauge doesn't measure pressure, as we are using it. It measures expansion of the chamber. Chamber measurements and some hidden calculations give pressure. Pressure between the bolt and the CB 'should' be the same so there is no reason for a long or several sensors. But velocity might be measured by multiple sensors.

[303Guy]

I have heard of multiple sensors being attached. The secondary sensors would confirm the primary trace values and would indeed measure the velocity - with a little bit of math.

[Doc Highwall]

popper, the RSI unit I have converts the strain into direct pressure in P.S.I. and gives both Time and Pressure for the whole trace till the bullet exits the muzzle.
67345

[popper]

converts the strain into direct pressure in P.S.I. No disagreement intended it just takes some calculations. I was merely stating how they work. Different from a direct 'pressure' load cell measurement. I've derived fps from pressure measurements, I was thinking more about time of transit between 'bumps' of pressure when the bullet passes.

[Doc Highwall]

popper, the trace I posted above shows where the bullets left the barrel where the + is on trace at about 1.3 milliseconds. There is also a lot more data given that I did not post like barrel temperature, barometric pressure, area under the curve.
67372

[303Guy]

On those five traces, note the difference in time until muzzle exit. There's no way of calculating velocity from them, the barrel times are essentially the same with exception of the first and lowest pressure trace. What's interest to me is the shape of each trace. Those show the relative rate of rise of pressure and relative muzzle pressure.

67379

Now this is where it gets suspicious. The secondary spike is occurring after the bullet has left the muzzle!

Now here's a little bit of information to think on - for that high pressure spike to register on an externally mounted strain gauge means the chamber over which it is mounted is expanding very rapidly indeed. And it doesn't crack the epoxy gluing it down? I coated a barrel with polyester resin - the type used in fibre glass reinforced resin - blew off with the first low pressure shot! Besides, a strain gauge is an electrical device which means it will respond to an electrical pulse. I have a calculator mounted on the loading bench which makes beeping sounds in response to touching a boolit against a transformer terminal even when that calculator is switched off. The strain gauge which is made of the same stuff as the internals of that calculator with silicon chips and connecting wires. A bullet being driven down the bore must surely develop a significant electrical charge. That's only one possibility, as unlikely an explanation as it may be. Just think, an extreme pressure excursion occurring after the bullet exits the barrel in one case and before exit in another yet no primer rupturing or excessive flattening, cratering or whatever is reported in either case (six cases actually). Then again I've mentioned before about a case getting stuck by the neck expanding into rust pits in the chamber while the primer shows nothing at all. There was probably a localized pressure spike at the boolit base. None of those boolits were recovered for base examination but they did shoot accurately.

[waksupi]

Would the sudden pressure back into the barrel cause the second spike? A bullet exiting the tube must create a hell of a vacuum for a millisec. I would think it would be quite abrupt, and cause a secondary discharge of thrust.
I haven't had time to keep up on this interesting thread, just tossing out ideas.

[Doc Highwall]

In post #102 by 303guy, this is what was said in regard to the pressure trace for Nosler 7-STW Factory ammo.

This interesting pressure trace was taken while shooting factory ammo. It was surely tested using standard SAMI protocols but if the lab used a peak capture meter, not an oscilloscope, they would not have seen the severe secondary pressure "if" it occurred in their test barrel.

The exit time markers are where they should be for a standard barrel. Secondary pressure events are typically less severe and INSIDE the end of a long barrel. (See tech article.)

We believe this to be a gross example of "deflagration" or unburned powder burning AFTER the bullet exits. The scary bit is more than 81,000 PSI is read by the strain gage located over the chamber! It is impossible to know if the entire length of the barrel was exposed to this pressure. But if it was, then the load is approaching the yield strength of thinner parts of the barrel and "could" expand the bore.

Ironically the exit timing, velocity S.D. and accuracy was great for factory ammo... but it does light up half the county when fired at night.

[Larry Gibson]

Larry, the strain gages that come with the RSI unit have a gage calibration factor to input into the program.

Could be the same gauges used for the Oehler?

Larry Gibson

[Larry Gibson]

Doc

I don't think those are really "secondary pressure spikes".. I had similar ones once and called Dr. Oehler. He asked several questions regarding the physical set up of the equipment and the bench used. When I moved the equipment to a more prtected psition from the muzzle blast and the shock vibrations created by the bench to the equipment the spikes, similar to yours, went away. Only happened with some guns, cartridges and loads.

The secondary pressure spikes I refer to occur before muzzle exit. Equipment set up has no effect on those.

Regarding psi along the barrel; You can graph the time/pressure curve (trace) and get a real close estimate of the psi at any point in the barrel.

Also note; peizo/transducers also do not measure the psi "directly" as the cartridge case is expanded by the psi to push against the transducer which converts the pressure of the push to electrical impulse which is then "translated/converted to psi by the computer program. Pretty much the same as the strain gauge. Dr Oehler conducted a test where he had a C.U.P. device, 3 different transducers and 3 different strain gauges (hooked to a M43 and M83s). He could then compare all those systems for each test shot fired as they all measured the same psi/trace for the same test shot. The results show the accuracy of the strain gauges compared to the C.U.P. and transducer methods.

Larry Gibson

[Doc Highwall]

Larry, go to this page and you will see the secondary pressure spike before bullet exit.

http://shootingsoftware.com/

[popper]

67474
Interesting dip in pressure on this one, not sure what causes it. Ideas? Most of my traces have a pressure divit toward the muzzle. I won't go into reflected wave theory. Most of my guns have a tight bore at the muzzle. Load cell is usually a piezo between the test device and a reaction block (relatively large mass) to directly measure pressure.

[Larry Gibson]

Larry, go to this page and you will see the secondary pressure spike before bullet exit.

http://shootingsoftware.com/

Interesting! A test I ran of Winchester white box M193 gave 65K+ psi with a correspondingly high velocity. I gave up after 5 rounds. It also gave indications of a secondary spike but the test barrel was 21" so perhaps that negated it(?).

Larry Gibson

[Larry Gibson]

popper

I see lots of traces like that; usually associated with medium or slow burning powders on the low end of consistent ignition and burn.

Larry Gibson

[DrCaveman]

I know this is a little off topic of where this thread has gone, but i think it might be a useful aspect of the ultimate conclusion.

Im reading Sixguns for the first time, and in the chapter titled 'cartridge reloading' Keith states a balance point for several powders. bullseye and unique are the ones i use, he also mentions dupont #6 and #80. Not sure what today's equivalents are for those two, but someone here surely knows.

He states that bullseye has a balance point of 9000 psi, extending 4-5000 pounds below and 3000 pounds above. Unique has balance at 13000 psi, 4000 pounds above and 'very little below'.

Taking for granted that he is right (and my respect increases with the more of the book i read).....

Interesting that two popular powders, used in a lot of the same cartidges, would offer this disparity in performance. Simply put, and common knowledge to most: unique doesnt shoot as well when downloaded, bullseye does well from max loads down to target loads. He is just putting numbers to this phenomenon.

What i anxiously awaited in the book was a balance point stated for 2400. I never saw one. Why not? There must be an ideal pressure, then a low and high extreme for acceptable performance. This number should be related to powder charge, cartridge, and seating depth, of course. But also probably will be influenced by barrel length and even maybe boolit fit.

Seems that he was talking about complete ignition of the powder, 100% combustion in a perfect scenario which will never actually happen but you can get close. A 'balance point' and edges of the curve must exist for all these powders, right?

No unburned powder means no secondary spikes?

Maybe not so simple because various barrels will be more accurate at certain velocities, regardless of perfection of powder burn.

Maybe this is not helpful at all. But i am curious what the 'balance points' are for all these powders out there. Loading manuals should have that list

[Doc Highwall]

You can have a secondary pressure spike and still not leave any un-burnt powder in the barrel. With short barrels I would doubt you could see a secondary pressure spike as the un-burnt powder would be blown out the barrel with the bullet and is probably what makes for a large muzzle flash.

[303Guy]

That's an interesting aspect, DrCaveman. Thanks for introducing it. I've been thinking some vague thoughts along those lines and now you've clarified them. And I agree, the loading manuals should have a list of 'balance points' for the powders we use - make that all powders.

An observation I've made is that a powder won't burn well at low loadings which equates to low pressure then burns well as the loading goes up then reaches a zone where pressure begins to go north fast. Thinking of case capacity and powder charge, I keep hearing about the 30-06 doing well with cast using Unique and I'm thinking of a balance between powder charge and case capacity and given the relatively low expansion ratio of the 30-06, the generated pressure will be maintained for a fair distance down the bore producing reasonable velocity with a low peak pressure. I'm referring to initial volume over final volume. A higher expansion ratio rifle would not be able to achieve those velocities with such low pressures and perhaps not allow the time for consistent burn.

I have a heap of Bullseye equivalent and find it too fast for the Brit. Likewise I find Trail Boss too fast but at lower loadings things seem to improve. My suspicion is that all the powder burns before the boolit moves vary far so case capacity is all there is to absorb the hot gasses formed. This is where my fuzzy idea came in - the case needs to be able to contain the gasses formed by combustion before expansion effectively begins. Too little powder produces too low pressure and too much produces a pressure spike. The balance. Part of that balance might include the boolit mass or weight. A lighter boolit seems to be better for a smaller case with faster powder.

If I had a pressure trace machine I could have a lot of fun finding the balance for different powders and boolit weights!

[Doc Highwall]

303Guy, look at my post page 3, post #44 showing the bore volumes for equal length barrels and how it relates to pressure drop off.

[popper]

There's no way of calculating velocity from them Yes, there is. Area under the curve is energy. The velocity can be calculated from the mass and energy. I read somewhere that this energy is divided into propelling the boolit, heating the barrel, frictional losses and expanding the barrel. The source indicated it was somewhat caliber and powder independent. The powder burn rate determined the chemical efficiency of creating the pressure.

[felix]

You read that here, Popper! ... felix

[popper]

Felix - World's Great Rifles, by Roger Ford (1998, Brown Packaging Books, Ltd., London). 20-30% goes to fps, 40% muzzle blast, 3% friction, 30% heating(and expanding the bbl).
Don't know his source.

[felix]

Yeah, that would be a good (and expected) average to quote using normal components (including gun). The statistics would change somewhat if StarWar plastics were involved giving more energy directly to the projectile. ... felix

Information probably came from such studies via JohnsHopkins performed for the Navy between the big wars. ... felix

[popper]

I was amazed at the 70% being 'wasted' as we would consider. Thinking about it makes sense though, Muzzle blast is the hot gasses that don't do any work on the CB ( but do on the air outside). Another comment from that source was that powder gives ~ 180 ft-# per grain, properly burned. Also, twist uses 0.2%, but I assume this is a slow twist value. I've read about the amount needed to engrave but forgot that value. It wasn't too high, even for jacketed. I've over estimated friction, under estimated bbl energy. Anybody have the Powley equations?

[303Guy]

I'm surprised at the value given for heating the barrel (and expanding). The barrel doesn't get that hot from each shot. Barrel expansion is elastic so does not retain much energy but I suppose the energy it does absorb is only released after muzzle exit. Nothing said on recoil energy?

I've had bullets stop in the bore only to almost drop out once cooled - the jackets showed heat scorching, indicating lack of thermal contact with the lead core (those bullets never shot accurately with full power loads).

I've had a hornet load that heated the barrel as much as a 303 does. Velocity was pretty high. I increased the powder charge a small amount and that heating went away. Velocity went up but I don't know by how much - noticeable on the range in that it was slightly flatter shooting. That was using Lil'Gun.

Oh, how does one differentiate frictional energy from barrel heating energy? Frictional energy is heating energy!

[popper]

I am guessing but think the recoil is counted in bbl heating. Case, chamber & bbl mechanics are reasonably easy to calculate, don't expect me to. Expansion takes energy, relaxation doesn't. Friction is calculated from coefficient of friction, yes it is heat but not that much and part of the heat is in the CB. In the context of this thread, we want proper pressure to get all the energy out of the powder without breaking anything. The time curve is important to keep acceleration increasing until the end of the bbl. Bbl temp is a function of bbl cooling and rate of fire. Thermal expansion of copper is really large.

[303Guy]

Well, one thing for sure is a large portion of the energy is lost, no differently than an internal combustion engine. Actually, a gun is an engine!

I've been trying to figure out how to determine the rate and duration of pressure rise. Well a pressure trace will just have to be acquired, but what to do in the meantime. Well, the only thing I can do is check boolit base deformation then get out to the range and see how that load, boolit and alloy performs.

[felix]

The oil companies did those heat studies back during the 50's. The overall conclusion was that the typical 6 and 8 cylinder engine-trans-axles-tires stole 65-70 percent of the energy destined for road propulsion. The deal in jet/rocket engine design is how much pressure generation can be RETAINED (for continuous operation ... think turbine here), and then released into what direction and for an amount of propulsion. ... felix

[DrCaveman]

Felix that is interesting

Im probably gonna make several errors here but bear with me and correct where needed.

Gonna try to create a car-gun analog

An automobile propulsion system starts with the spark (trigger pull followed by primer ignition). This ignites the gasoline/air mix (powder charge density) and the resultant pressure created is relative to the octane level of the gasoline (powder burn rate).

This in turn forces the cylinder downward (boolit release from neck tension and crimp) which then rotates the crankshaft (boolit enters leade and begins rifling rotation). Then the transmission converts the torque into something useful (the particular rate of twist).

The drivetrain is then spun (boolit obturation, final seal) and power is transmitted to the axle through the dfferential (peak powder burn pressure) and then the wheel bearings and tires provide the contact with the pavement (boolit lube and barrel condition)

Plenty of holes in my thinking im sure. But maybe this helps provide an analogy-one which many people here understand veeeery well- that can help pinpoint energy losses and more efficient powder pressure utilization

[303Guy]

If I may add my analogy; The piston travel down the cylinder equates to the boolit travel down the bore. Work done per piston power stroke equates to the energy gained by the boolit. Exhaust valve opening equates to boolit exiting the muzzle. Ignition remains the same. The octane rating analogy of powder burn rate is a good one. The fuel in a piston engine burns at a rate which is a function of flame front velocity and turbulence and who knows what else. Some fuels burn slower than others and some self ignite from pressure and hot spots forming two (or more) flame fronts. Engine knock is the one that (from multiple self ignition points) is one that may equate to pressure spikes although the mechanism may be different.

The power delivered to the road would equate to the boolit impact energy. A boolit does have power on impact which probably is more important than the impact energy. Power brings time into the energy transfer.

On expansion ratio and powder energy release and transfer to the boolit - if one considers a cartridge and barrel with two different boolit weights with the same powder, how does the barrel length affect the efficiency of the cartridge? For example, a short barrelled 303 Brit, which would be more efficient, a lighter boolit with a higher powder charge or a heavy boolit with a lower charge with each producing the same peak pressure?

[popper]

Yes Felix, flywheel power vs wheel power is vastly different. That's why they changed to wheel dyno measuring instead of the early prony brake type equipment. I will note that octane rating is anti-knock rating, not associated with burn rate. Combustion chamber design - wedge, hemi, L, T, valve size and path, etc has everything to do with burn rate and pressure. Not sure I'd take the analogy of engine vs gun very far. If you have the pressure & fps measuring equipment I think they will help developing a load quicker but most of us are forces to experiment with down range performance and CB recovery (thanks to those that can - much useful info).

[felix]

Yeah, Popper is more correct in what he has said. Octane rating belongs mostly to ignition characteristics of the gas, and very little to the heat (neither maximum or average) generated or propagated to the air which propels the piston. We "step" on the air, not the gas; it's the carb's job to mix enough gas for the amount of air (sucked or injected) into the cylinder. The timing of ignition is regulated by the octane rating AND the the piston's compression taken TOGETHER. Todays' computers do a pretty fair job of making an engine run just right for mating the individual car components chosen for an APPLICATION. Sensors (measurements) are the biggest problem by far just like for guns. ... felix

[jackmanuk]

i used some 4227 in my 308 , i only made up 5 rounds to try but it seemed good , burned clean no mess in barrel at all , compared to my 44 mag that ends up full of shiz after 1 round , so i made up 100 rounds with 28 ( ish ) grains on top of some amax 165 and matchking 155 ..... and i think some 135 and maybe a 185 too ..... cant remember but im sure il find out on the range :)

[303Guy]

I can't see anything wrong with 4227 other than the low load density (possibility of double charging). I'm not sure how it performs with j-words though. There is a stiffer resistance at launch which may push up pressures some. For cast it seems about ideal and it does burn clean in a longer barrel.

[Larry Gibson]

Be very, very careful not to double charge with those j bullets using 4227. Also double check the powder level of all charges in the case in case "bridging" happens. Going a "Bridge To Far" was disasterous for the Brits and could be for your rifle too.

Larry Gibson

[303Guy]

I wish they would make 4227 or similar in bulky form like Trail Boss. I like 4227 - what's the other one? H4198? H4198 is put above Lil'Gun followed by H4227 but one cannot put a burn rate on Lil'Gun. In the 303 Brit it's something like twice as fast as H4227 but in the Hornet it's quite slow (but does it only perform in the Hornet!) Anyway, in the Brit I use about 45% load density under a 208gr boolit with filler (wheat bran) and that produces about starting load pressure. Take away the filler and use Dacron and the load density can be increased - possibly to 50%? Double charging would be obvious if seen but powder bridging could escape unnoticed and as Larry puts it - a bridge too far!

[Bullshop]

I wish they would make 4227 or similar in bulky form like Trail Boss. I like 4227 - what's the other one? H4198? H4198 is put above Lil'Gun followed by H4227 but one cannot put a burn rate on Lil'Gun. In the 303 Brit it's something like twice as fast as H4227 but in the Hornet it's quite slow (but does it only perform in the Hornet!) Anyway, in the Brit I use about 45% load density under a 208gr boolit with filler (wheat bran) and that produces about starting load pressure. Take away the filler and use Dacron and the load density can be increased - possibly to 50%? Double charging would be obvious if seen but powder bridging could escape unnoticed and as Larry puts it - a bridge too far!
Changing the shape/size of the powder kernels changes the burn rate. For instance I understand that IMR 4756 and 4759 are the exact same formula only different in size/shape of kernel so burn or are consumed at different rates.

[popper]

a balance point stated for 2400. I never saw one. This powder is interesting. It's the only one I get vertical stringing at lite loads. The holes are round, so stability is OK. IIRC, 5 shots over the chrony gave ~ same fps, it would take 400 fps diff for the 3" drop. Shooting from a levergun so I could hold it 45 deg to see if it's bbl harmonics. Base damage should give a scattergun target - didn't, just vertical. Unique doesn't do it so I assume it's not flinch or recoil response. Bbl was warm as I'd been shooting regular loads. Filler doesn't matter, from earlier tests. Read all the BR & long range shooters comments, like primer strike, primer seating, H.S., bedding, etc. Yea, maybe @ 600yds, but NOT @ 50! Actually, other than bbl harmonics, I see no real reason for any accuracy diff. (due to load) until the alloy fails. Of course I'm wrong, BUT? I know Marlin had to work on the tube mount of the 308MX to get it to shoot right with the FTX.
edit: After mulling my comments overnite, I'm pretty convinced that 2400 burns erratic in low loads causing erratic bbl harmonics and lousy accuracy. Kind of like a V8 with bad plugs. Dacron doesn't help but SG buffer may. Only other that I can reason is primer pressure vs powder pressure but the results are the same.

[stephen m weiss]

Wow popper, it sounds just like alliant 1200r. its very dense with variable size flattened spheres. Quite fast. In my 223 I get vertical stringing, 1moa horizontal and 4 moa vertical, in light loads. My conclusion was grit in the barrel. The first shot is typically right on. The grit will always sit on the bottom, so when you bullet picks it up and starts spinning it around, it will always come out in about the same orientation, if the stuff is mostly at the back towards the chamber, like in mine. It's not speed. At the speed i was firing, 2 inches is the whole drop, cant change drop by the whole drop haah. If it were barrel harmonics, it would be proportional to the driving force. So, at low loads, real small. 4moa is not real small. I am not completely sold on the grit explanation, but I do suspect something about the way gravity pulls the charge and debris to teh bottom of the barrel.

I need to make up some more and bore brush in between shot to see if that fixes it or makes it worse. I was playing with making sks rounds this week so no need for filler.. just less room in the brass.

[rbrtdun]

Varget and H4895 are both stick powders, which are said to light easier due to have less aggressive deterrent coatings. If that means anything. And 4895 has always been one of the canonical cast-bullet powders in the .30-06, going back to the '50s, if what I read in the old sources is accurate. It's a good deal slower than Varget.

The comments about light loads of Varget were on a thread here regarding the 7.5x55, my remembery is trying to tell me.

I have some 165 gr pb cast that I am trying to work up loads for a .30/06. I have tried the slower powders from an old Lyman book and gotten poor results. Can you suggest a good load using H4895 with 165 gr plain base bullets?

[iplaywithnoshoes]

If I may add my analogy; The piston travel down the cylinder equates to the boolit travel down the bore. Work done per piston power stroke equates to the energy gained by the boolit. Exhaust valve opening equates to boolit exiting the muzzle. Ignition remains the same. The octane rating analogy of powder burn rate is a good one. The fuel in a piston engine burns at a rate which is a function of flame front velocity and turbulence and who knows what else. Some fuels burn slower than others and some self ignite from pressure and hot spots forming two (or more) flame fronts. Engine knock is the one that (from multiple self ignition points) is one that may equate to pressure spikes although the mechanism may be different.

The power delivered to the road would equate to the boolit impact energy. A boolit does have power on impact which probably is more important than the impact energy. Power brings time into the energy transfer.

On expansion ratio and powder energy release and transfer to the boolit - if one considers a cartridge and barrel with two different boolit weights with the same powder, how does the barrel length affect the efficiency of the cartridge? For example, a short barrelled 303 Brit, which would be more efficient, a lighter boolit with a higher powder charge or a heavy boolit with a lower charge with each producing the same peak pressure?

Engine knock/auto ignition is a good analogy for detonation within the chamber. You are essentially experiencing local pressure spikes which are throwing off any desired differential pressure down the length oh the cartridge, the difference being that chamber pressure is at atmospheric before the primer or 'spark' occurs occurs.

A note on the efficiency of the barreled action and load combo (likely you have found this by now), efficiency related to barrel can be defined in several ways when referring to the full firing event.

We can try this: Peak thermodynamic efficiency for a given load/barrel length is achieved in two particular theoretical instances:

1. Infinitely low friction in the barrel given that the powder has burnt quickly in the chamber due to proper neck tension etc., where the barrel is long enough that the pressure at the muzzle is at atmospheric at exit.

2. Some consistent friction throughout the barrel, with some barrel length that still allows for positive acceleration of the bullet just before exiting the muzzle.

In both cases, the main dissipative mechanism (assuming a perfect seal) is heat transfer to the action/brass, rotational energy impacted on the bullet and bullet deformation, while the second case has added energy loss due to friction. The simple reason that we cannot achieve either of the two cases is because production barreled actions cannot take the chamber pressures resulting from all possible gases expanding all at once (100% burn) before the bullet leaves the cartridge. The compromise therefore boils down to small quantities of fast burning powder, or large quantities of slow burning powder. In a way, the fast powder is going to be more efficient for a given barrel length, given that the heating value of the two powders is roughly identical, since the activation energy of the slow burning powder may be higher and pressure is lost as the bullet travels down the barrel. This could be the rough equivalent of an engine with delayed ignition.

What you are balancing is pressure, heat, powder burn rate, friction and several other variables in order to achieve a super efficient load combo, which requires a minimum amount of powder to achieve an absolute performance directive. Without knowing exact numbers, it makes some sense as to why slow burning powders maximize the performance of jacketed projectiles, and cast bullets benefit from lower quantities of fast burning power. Other variables such as projectile weight, alloy hardness, fitted diameter, neck tension and dead space in the case can fill the performance space between the these two loading types.

I am missing a lot of numbers and specific effects here but this is just a quick 5 minute fundamental thought process. Quickload gives you the information you want to some percentage of certainty in some loading conditions since it benefits from a relatively high time step and can calculate all of these states quickly and simultaneously. Your best answer will come from that software I think.

Perhaps a last side note on load density and pressure spikes. It's likely that load density's effect on cartridge dimensions is like that of some blunt object hitting sand. The primer's flame/pressure front can be dissipated sufficiently at certain load densities that the bullet will not be prematurely pushed out of the case before ignition. At lower load densities, the powder can be pushed forward like a hammer or compress air like a piston, causing said detonation or pushing the bullet out too early. When the load density and compression are too high, the pressure hits the powder column as if were a solid, thereby transferring impact from pressure instantly. At this point, granular physics likely determines which load density is best for each powder type.

I am wondering any of this makes sense.

shoe

[Bama]

a balance point stated for 2400. I never saw one. This powder is interesting. It's the only one I get vertical stringing at lite loads. The holes are round, so stability is OK. IIRC, 5 shots over the chrony gave ~ same fps, it would take 400 fps diff for the 3" drop. Shooting from a levergun so I could hold it 45 deg to see if it's bbl harmonics. Base damage should give a scattergun target - didn't, just vertical. Unique doesn't do it so I assume it's not flinch or recoil response. Bbl was warm as I'd been shooting regular loads. Filler doesn't matter, from earlier tests. Read all the BR & long range shooters comments, like primer strike, primer seating, H.S., bedding, etc. Yea, maybe @ 600yds, but NOT @ 50! Actually, other than bbl harmonics, I see no real reason for any accuracy diff. (due to load) until the alloy fails. Of course I'm wrong, BUT? I know Marlin had to work on the tube mount of the 308MX to get it to shoot right with the FTX.
edit: After mulling my comments overnite, I'm pretty convinced that 2400 burns erratic in low loads causing erratic bbl harmonics and lousy accuracy. Kind of like a V8 with bad plugs. Dacron doesn't help but SG buffer may. Only other that I can reason is primer pressure vs powder pressure but the results are the same.

There is a research paper entitled "Dynamic analysis of a guided projectile during engraving process" which sheds a lot of light on the dynamics of a projectile as it is fired down a barrel. It has details of a lot of items I had never even considered such as the bullet starting and stopping or trying to initially which sets up a vibration in barrel and what was done to reduce the occurance. It was done by an engineering group in China--bullet was in 20 in range. They were able to install all type of sensors. Search key was "bullet engagement"

[popper]

Bama, it is a good read and has some generalized concepts. It was also written for guided projectiles like the 115 I worked on. Our engraving time is more like micro sec vs his milli sec. He does make a valid point, the the acceleration is not constant but vibratory like a jack hammer - as the boolit gets engraved.
His findings that the CG moves back led to army studies that found the lead core of rifle bullets would separate from the nose as momentum caused it to 'flow' into the grooves. That means our cast noses don't just slump side ways but actually get shorter as alloy flows into the grooves.
That 115 project was to put laser/IR guidance on the nose. IR detector had to see through the laser detector. Don't ask how it was done.

[Norske]

To answer the original question of this thread, shotgun powders are designed to burn cleanly and completely at around 10,000 psi. Red dot has long been favored in 45 ACP, Unique can be used for almost any performance level in a 20 gauge, and most handgun cartridges. It's even good for some rifle/cast bullet loads. However, as Ol' Elmer pointed out, Unique will melt cast bullet bases at higher pressure loads, hence his favoring 2400 powder (also useful in magnum shotgun loads). Richard Lee has a good section on bullet hardness vs. peak pressure in his 2nd edition loading manual. Quickload software is from a German chemical engineer and his bomb calorimeter. The new editions are much better than the first because of extensive verification using European gun maker's test barrels. So it's not as only predictive as it used to be, there is extensive pressure testing involved now.
So, good sources of pressure tested printed load data include the aforementioned Lee book, Lyman's cast bullet loading manual, Hodgdon data, internet or annual manual, and Western Powder's printed manual. Some of these even mention powders that aren't very position sensitive.

[pukester]

You should call Alliant or Hodgdon or whoever's powder you are interested in and ask them. They are always quite helpful and they will be the most reliable source. Your question needs a reply from a powder company about a specific powder. I do know that when it comes to smokeless powder,..the reason it works is because it is in a confined space. The more you unconfine (for lack of a better word) it, the more you get away from properties that make it what it is. I hear black powder is totally different but have never used black powder.

[Cosmic_Charlie]

I was trying to figure out what I could use 8 lbs. of 1680 for since it is available now.

[panhandle]

I am very new to this forum and still trying to work out a consistently useable load for both 30-30 and 30-06 using a 173 grain cast bullet I have a mold for, I have tried 2400, 748 and unique so far with gas checks and sized a thousandth or two over bore dia. I'm liking the groups OK but finding chambering difficulties after 6 to 8 rounds. not sure what's wrong. I'm coating with hitec coating. bore looks clean with the unique in my 30-06 but must be getting chamber buildup