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Thread: Powder Burn and Pressure Relationship

  1. #121
    Boolit Master popper's Avatar
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    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.

  2. #122
    Boolit Master 303Guy's Avatar
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    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.
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  3. #123
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    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
    felix

  4. #124
    Boolit Master DrCaveman's Avatar
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    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

  5. #125
    Boolit Master 303Guy's Avatar
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    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?
    Last edited by 303Guy; 04-29-2013 at 01:41 AM.
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

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  6. #126
    Boolit Master popper's Avatar
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    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).
    Whatever!

  7. #127
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    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
    felix

  8. #128
    Boolit Man jackmanuk's Avatar
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    Red face

    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

  9. #129
    Boolit Master 303Guy's Avatar
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    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.
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  10. #130
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    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

  11. #131
    Boolit Master 303Guy's Avatar
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    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!
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

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

  12. #132
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    Quote Originally Posted by 303Guy View Post
    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.

  13. #133
    Boolit Master popper's Avatar
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    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.
    Last edited by popper; 10-04-2013 at 10:08 AM.
    Whatever!

  14. #134
    Boolit Man stephen m weiss's Avatar
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    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.
    Free to live, Free to die, Free to till the earth, And see the sky!

  15. #135
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    Using H4895 with cast in .30/06

    Quote Originally Posted by uscra112 View Post
    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?

  16. #136
    Quote Originally Posted by 303Guy View Post
    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
    Last edited by iplaywithnoshoes; 03-18-2017 at 12:25 PM.

  17. #137
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    Quote Originally Posted by popper View Post
    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"

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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