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Thread: Powder Burn and Pressure Relationship

  1. #1
    Boolit Master 303Guy's Avatar
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    Powder Burn and Pressure Relationship

    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?
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

    ''Assume everything that moves is a human before identifying as otherwise''

  2. #2
    Boolit Master DrCaveman's Avatar
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    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

  3. #3
    Boolit Master uscra112's Avatar
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    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
    Last edited by uscra112; 03-31-2013 at 07:06 PM.
    So long, and thanks for all the fish.

  4. #4
    Boolit Master
    Doc Highwall's Avatar
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    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.

  5. #5
    Boolit Master 303Guy's Avatar
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    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.

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    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.
    Last edited by 303Guy; 03-31-2013 at 11:21 PM.
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

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  6. #6
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    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.

  7. #7
    Boolit Master uscra112's Avatar
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    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!
    So long, and thanks for all the fish.

  8. #8
    Boolit Master Rocky Raab's Avatar
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    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.

  9. #9
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    Quote Originally Posted by uscra112 View Post
    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.

  10. #10
    Boolit Master


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    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.

  11. #11
    Boolit Master 303Guy's Avatar
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    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
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

    ''Assume everything that moves is a human before identifying as otherwise''

  12. #12
    Boolit Master 303Guy's Avatar
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    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.
    Last edited by 303Guy; 04-02-2013 at 02:30 AM.
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

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  13. #13
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    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!

  14. #14
    Boolit Master 303Guy's Avatar
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    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?
    Last edited by 303Guy; 04-02-2013 at 12:46 PM.
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

    ''Assume everything that moves is a human before identifying as otherwise''

  15. #15
    Boolit Master



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    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.
    Marty-hiding out in the hills.

  16. #16
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    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.

  17. #17
    Boolit Master
    Doc Highwall's Avatar
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    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.

  18. #18
    Boolit Master 303Guy's Avatar
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    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.
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

    ''Assume everything that moves is a human before identifying as otherwise''

  19. #19
    Boolit Master uscra112's Avatar
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    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.
    So long, and thanks for all the fish.

  20. #20
    Boolit Master uscra112's Avatar
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    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.
    So long, and thanks for all the fish.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check