For the experts out there, does barrel length for a given caliber change what powder will provide better speed? In my case is there a benefit to using a somewhat faster, or slower powder, when using a shorter barrel (21" 338-06)? Not suggesting going outside the powders that typically work with a given caliber, just maybe leaning towards the faster end of those that would normally be considered for the 338-06. H4350 and RL17 are what I've been using, and they have worked well. Just curious if I should consider others (I have Varget and H4895 laying around).

I should add, I'm using 210 and 225gn bullets.

No; you get the best speed by putting as much chemical energy (burned powder) behind the bullet as you can. To do this safely, you have to select a powder speed that prevents a case full of powder from completely burning until the bullet is far enough down the barrel that the space behind it can hold these gases at a safe pressure. Powder burn is complete (more or less) with the bullet less than a foot down the bore.

Let's look at this step by step:

1) First, all the powder that's going to burn will burn within inches of the case mouth, much less than a foot. Fast-burning handgun powders will burn within less than an inch; the slowest burning rifle powders within 2-4 inches.

2) If the pressure is correct for the powder in question then almost all will burn. Let't call it 99%.

Some rifle powders are designed to burn best at 50,000 psi or so, others (usually the slower ones) at 60,000 psi. This is assuming we're talking about conventional bottle-necked cases designed for modern bolt-action rifles.

My own experiments, as well as those of many other people, indicate that the "best" (producing the highest muzzle velocity) powders for a given cartridge and bullet weight will be the best powders in any legal barrel length, which in the U.S. is 16".

The powder/bullet combination that will lose the least velocity in a short barrel is a slow powder with a heavy bullet.

Thanks JB. Works for me. I see no reason to change from RL17 and H4350.

I'm curious, John, how was it established that powder ceases to burn by about 4 inches of bullet travel?

I've read this elsewhere, but it's not obvious to me how it came to be known. To measure it physically is daunting. One not only needs to know pressure accurately, but bullet position in the barrel as well, and one also needs a handle on convective and radiative heat losses to the barrel and chamber.

It seems agreed that peak pressure occurs by about 4 inches of travel, but that does not necessarily imply gas production has ceased by then.

If established, this could explain why the QuickLoad simulator can underestimate peak pressure. For a 180 gn bullet in a .30-06, it estimates even a powder as fast as Re-15 is only about half burned by the point of peak pressure, and that a 90% burn comes about 9 inches down the barrel. It's mathematical estimations are hardly exact, but to track as well as it does the actual trends of internal ballistics over such a wide range of cartridges, I wouldn't expect it to be in gross error.

Regardless, I find nothing to contradict the claim that with legal length barrels, barrel length does not select optimum powder speed.

Karl

It has been extablished various authorities (Homer Powley among them) that the peak of the pressure curve is where all (or almost all) of the powder is burned. As I recall, this was established partly by cutting back barrels and seeing how much unburned powder was left at certain lengths.

Some people are under the impression that the peak is caused by the bullet fully engraving in the rifling, but that happens almost immediately in front of the chamber.

To speak of such things where rifle powders are concerned, gets a bit tough because there�s so many rifle cartridges out there, which brings about a lot of variables. With handguns, it�s a bit easier because the sampling of both cartridges and powders is smaller. So let�s take a magnum revolver cartridge, say the more popular ones, such as .357, .41 & .44 magnums. With these powders, generally speaking it�s the slower powders that give you the highest velocities (H110/296 etc). This is true regardless of barrel length.

With rifles, you can�t make such a statement, because not always is it the slowest powder that gives you the highest velocities. But suffice to say, whatever powder gives you the best velocity in a 24� barrel, is probably going to be the one that gives you the highest velocity in a 16� barrel.

However, whether we�re talking revolver or rifle, that increased velocity in short barrels often comes at the expense of greatly increased noise and muzzle blast; which is not always desirable for this shooter.

The shape of pressure traces clearly indicates that burning continues past peak pressure, so perhaps barrel chopping experiments missed energy released inside the prodigious muzzle blast. Consider this trace from RSI's site:


If gas production had ceased by the point of peak pressure, the fall off in pressure would be similar to that of an adiabatic expansion. Such curves have sharp fall offs, yet the traces show a very broad and rounded fall off.

This would have been noticed even in the 1920s, so I remain at a loss to explain the information at hand.

For grins, I had QuickLoad simulate a burn of enough Varget to produce about 44 ksi peak pressure. It's estimated time trace is remarkably similar in shape to that of the RSI traces. It figures a fair amount (15%) of powder remains to be burned as late as 0.7 msec. Both QL and the RSI traces show points of inflection (in the pressure traces) at about 0.7 msec, indicating the bullet is well out pacing the production of gases, to the point that the curve is starting to look like a simple expansion. At this point, QL estimates the bullet has moved about 6 inches with powder to go.

I wish I had the time and money to run proper experiments on this stuff...

I don't think I'd rely overmuch on QuickLoad. As brilliant as the program and its creator are, it is still software. That means that it will spit out pretty much what the assumptions and formulae you feed in create. Actual pressure traces are more trustworthy because they report what is actually happening.

BTW, I disagree with what 2525 says. If all the powder that is going to burn is ignited more or less simultaneously, then it will burn out more or less simultaneously. That occurs at the pressure peak; again, more or less.

Some powder never does burn. In a bottleneck case, it is probable that a "plug" of powder gets compressed and rammed into the back of the bullet at primer firing. That dense plug is too compact for primer gasses to penetrate and cause ignition. Only the rearmost surface layer can and will burn. Any residual burning from such powder kernels might explain why the post-peak curve is shallower than we might expect. Note, however, that with the pressure dropping, any post-peak burning is much less efficient than otherwise simply because the pressure is below the optimum for that powder. That's why we can say that the peak marks the end of effective burning.

In any event, by timing the pressure curve, it is quite simple to know where the bullet was at any given point on the curve.

I won't rely on the QuickLoad outputs as gospel, but the math behind it is beyond mere assumptions; the formulas it uses are based on empirical research. Having coded software simulations of physical processes myself, I'm aware they can be embarrassingly inaccurate, but I'm also aware they can provide insights that empirical research can be slower to highlight.

It wasn't until I compared QL's traces to that from RSI that it dawned on me that RSI's traces showed it's not possible for the burn to have been completed near peak pressure, as I outlined above. Once the burn is complete, the pressure trace will be concave (as viewed from "above" the curve). Instead, it is convex over half the trace.

How would the pressure show the drop with the bullet still in the barrel? Once pass peak pressure there is a slow decline due to the lack of more usable pressure being added by burning powder and by the bullet progressing down the barrel.Rick.

No, the peak of the pressure curve is caused by the powder burning and creating MORE gas. Once the amount of gas is stable (because the powder is burned) then the pressure curve starts downward. The gas is expanding, because it's hot, but no more is being created by burning powder. The pressure curve drops because the volume of the bore increases as the bullet travels further along.

No, that the curve starts down only indicates that the bullet is creating volume faster than this volume can be filled by the burning of the remaining powder. It does not prove gas production has ended.

Now, if there is no more gas (and energy) being released, then the pressure vs. volume curve will closely follow a shape of the form P*(V^k)=c. Plotted against volume, this curve is strongly concave upwards. We're looking at P plotted against time instead. Here, the bullet's acceleration will stretch out the curve, but I'm confident (which doesn't mean I'm correct!) it cannot invert the shape of the curve.

The RSI data shows a convex curve after the pressure peak.

I am most skeptical that the bullet could possibly create more volume by its movement than the powder can fill with gas. I think that's the flaw in your theory.

Any convexity in the curve after the absolute peak is due to the "tailoff" of residual propellant, but that is a minor and short-lived event, as evidenced by the faster (and concave shape) shortly after the peak.

The bottom line is that pressure builds as long as there is deflagration. By definition then, when the pressure ceases to build, burning has (essentially) completed.

I initially thought the same, but I'm willing to bet that 2525 was trying to say that the burning of the remaining powder was unable to sustain the same pressure as the volume expanded due to the now-moving bullet.

On the other hand, I think he may be incorrect in thinking the bullet is no longer accelerating once the powder has burned completely (or as completely as it's going to burn; there is usually up to 15% unbunred powder.) The bullet will continue to accelerate as long as the pressure behind it is greater than the resistance of the bullet against the barrel. The Delta Vee will be reducing as the pressure behind the bullet drops, but it's not going to be negative.

Rocky, I believe that what powder remains can't fill the void fast enough. The grains are smaller and present much less surface area, and this limits gas production, and once the pressure curve begins to fall off, the burning rate falls rapidly, compounding the situation.

What's this "tail-off," and if it is a minor and short lived event, then why does the curve remain convex for about .3 ms, which is on the order of the pressure rise time recorded?

FTR, I didn't claim the bullet stops accelerating; it most certainly keeps accelerating! The acceleration is why the pressure-time trace is flatter than the pressure-volume trace. It's because the acceleration is due to the pressure that I'm confident switching from a p-v curve (which I'm certain must be concave upwards) to a p-t curve will still leave you with a curve that must be concave upward (after the burn is done). Real curves are convex, so I believe burning continues--as QL predicts.

I've taken this discussion a bit off the topic, eh?

Nope, it's interesting. I'll just rephrase my question to what powder psi trace will provide the largest volume under the curve for a given bullet and barrel length, without exceeding max psi?

Although not specifically mentioned, the charts and graphs illustrated seem to relate to a certain case capacity, bullet weight and diameter and barrel length.

Said another way, a powder type balanced with the cartridge and caliber and bullet weight.

My question is, if we take it to the extremes and use a much lighter bullet, say 100 grains in a .30-06 and use the largest amount of the slowest burning powder that is safe to use, would all the powder burn before the bullet exits the muzzle?

Would it all burn within the first 5 or 6 inches of bullet travel.

It seems to me, to get the most velocity from a given cartridge, you would have to balance the powder burn rate with the bullet weight and case capacity.

The part about the pressure dropping after peak pressure. That is because the bore capacity is increasing as the bullet moves forward.

There is a name for this, but I can't think of it. It goes something like this--you have a sealed container with X amount of gas pressure inside it. You double the size of the container, and the gas pressure drops to 1/2X. If you half the size of the container, the gas pressure increases to 2X. This pressure rise and/or fall is also progressive and at a constant ratio.

That is the reason the gas pressure drops after it peaks in a barrel and the powder is no longer burning and producing gas.

But, as long as the pressure inside the barrel is greater than the pressure outside the barrel, the bullet will continue to accelerate.

That can also be what causes a gun to blow up. If the bullet is not moving forward fast enough to create more bore volume to keep the gas pressure in check, the gas pressure will soon overcome the available volume, pressures will rise, and if they rise high enough, something will let go.

2525,

It is a common misconception that the mere increase in bore volume versus the amount of gas is the total cause the curve drop off.

But why does it drop off so quickly? If mere bore volume was the answer the curve would drop more gradually, instead of at a definite peak. The peak (or just past it) is where powder has ceased to burn to any significant extent.

And to add to JB's words, the "tailoff" as I (and rocket engineers) call it is just what 2525 said: the last bits of propellant kernels burning out. There are always some that are slower than the others. A small percent of the powder can ignite late. The higher the loading density, the tighter packed the charge and the greater the distance from the primer, the larger that percentage can be. And some powder, as observed above, never lights at all.

But I think that the real experts in the field are almost unanimous that effective burning is signaled by the pressure peak. And I probably could have left out that "almost."

I just wanted to comment on the "charts and graphs" that somebody mentioned being shown here. There has only been one, showing a .30-06 with a 150-grain bullet and Varget. It is not anywhere near a maxiumum load, in fact the peak of any of the curves is around 44,000 psi, which is far below the peak (and most efficient) pressure for Varget, or many other modern rifle powders.

The pressure curve at 55,000-60,000 psi with most modern rifle powders shows a much steeper climb to the peak, and a steeper drop-off. I have looked at a bunch of Pressure Trace curves and at 55,000 to 60,000 psi the curve has a much more obvious peak.

So the "charts and graphs" are not plural, and the single one shown does not represent a typical load for modern bolt-action rifles.

"It is a common misconception..." JB, I must disagree that near peak pressure the rate of change of volume is insignificant. QL is predicting that at peak pressure, the bullet is already up to 1000 fps. That is 12 inches per msec which works out to an increase in volume of about triple the case capacity of the .30-06 every msec. The pressures in the RSI trace are above 90% of the peak for the .25 msec or so centered about the peak, so the volume increase is about 3/4 of a case during that time. This rate of volume increase coupled with decreased grain size remaining seems perfectly consistent with QL's figuring that the burn simply can't keep up with the bullet.

You ask why does the curve drop off so quickly, yet I ask why doesn't it drop more quickly. My claim is that if the powder were fully burned by peak, then the curve should fall off more sharply. Instead, we see a big dome that's roughly centered around the pressure peak.

As for a 60 ksi trace, had I one at hand, I'd be happy to look it over. That one on their web site was the first I came across. I'll see if I can't find one on their site tomorrow. I'm heading out for the evening.

Stop you makin me dizzy!! LOL

I have seen a bunch of 60,000 psi Pressure Trace graphs, created when I was using one. The peak goes up much more rapidly and drops of more quickly as well.

I am out of this discussion. This point has been proven by professional ballisticians over and over, especially Homer Powley at Picatinny Arsenal. But it is doubted over and over, like many old misconceptions. Now it is supposedly disproven by a computer program.

the short answer is .....NO!

Now it is supposedly disproven by a computer program.

Hardly. The program can only give suggestions as to what is going on behind the actual pressure traces.

I'll (try to) close with my original and unanswered question: how was it established that burn out comes near peak pressure? If someone will cite a reference by the real experts, I'll seek it out. My thermo professor did research in this field for the army, so the library there should contain many works on internal ballistics. Frankly, until this discussion, I'd never considered what happens near peak pressure, and I still haven't a definitive answer.

My friend, I am not going to do your research for you. As you seem to be the lone voice in opposition to accepted theory, it is up to you to come up with counter evidence. As far as I've been able to determine (and I'll say it yet again), the end of effective burning is signalled by the pressure peak.

I don't think there is that much difference in what everyone is saying. I think all he is stating is that not ALL burning is done at peak pressure, most, yes. Here is a picture of a 223 graph that includes bullet movement and velocity.



It definitely indicates there is still a small amount of burning past peak psi. Once the bullet has moved about three inches the volume of the combustion chamber (case + barrel behind bullet) has nearly doubled, yet the pressure has clearly not halved (actually only about a 20% drop) so something has to be happening. Clearly, this is only one example so take it for what it's worth. If the pressure graph showed the pressure dropping much more dramatically (as JB has stated he has obseved numerous times) that would certainly indicate a more complete burn at peak pressure. Time to go watch some gameday!

Powder can blow out the pipe unburned-this I know from experience. I've loaded .375 -300 grain bullets in my Mark V Weatherby. I've packed those 378 weatherby jugs with 116 grains of 7828 behind the 300 grainers. I set the charge off with the shiity CCI primers. The last 5 grains did very little in the velocity gains. Theoretically if I could get a good burn possibly if I had a longer barrel. (not sure on that)There is alot of smoke and stink after that stuff blows out the pipe. I don't have fancy graphs but I can tell when the I get that big puff of smoke coming out the pipe that I'm not achieving a good burn. I didn't have Fed 215 primers but I know they are a hell of lot better igniters than the CCI in the big jugs. Kids don't do this at home. Detached retina stuff!!!!!

CCI primers,eh. Now I know why H1000 and 7828 shot out smoke and smell of burning powder.
I am going to stick to Loads of 85-90% that are listed as max loads in the manuals.
Better groups for me. Not a rocket scientist, just a handloader.

................Whichever powders that are listed showing the top speeds from a 24" barreled 338-06, will also give you the best speeds from your 21" barreled 338-06. In other words, you load for that 21" barrel just as though you were loading for a 24" or a 26" barrel. The same is also holds true if loading for even the shorter tubes such as 20" or less.

Regardless of barrel length, whether from a 16.5" tube up to a 26" tube, the slower burners (where listed for a given cartridge showing greater speeds) generally across the board, will also give the better speeds in the shorter tubes.

RL 17 was primarily designed to give a velocity boost in the short mags. However, I read that it is doing well in other cartridges too.

Whatever is going to burn gets consumed within a few inches of the case. Barrel length makes no difference for the burn time/amount.

The hot pressurized gases in the barrel are doing their work, pushing the bullet at an ever-increasing velocity. How the gases do the work is a function of the type of powder but his work comes to an abrupt halt when the bullet gets clear of the muzzle. The amount of work done by these gases is predicated by the length of the barrel. Whatever work they were still able to do when the bullet uncorks simply contributes to the muzzle blast.

Thanks. I just want to get 2600 with a 225 Accubond or 2700ish with a 210 Scirocco II using a temperature stable powder. Should not be a problem. I've found that RL 17 works well in the 338-06. Nothing spectacular though. However, I caveat that with the fact that I don't have any 'official' load data to use as a guide so I am hesitant to push things. I have found that it gives the same velocity of H4350 but with one less grain of powder.

prm, the plot reminds me of one I saw years ago in an NRA book. Having bullet motion and pressure on one time plot makes analysis much simpler, as you have pointed out. Being the plot of simulation results, it won't settle the question.

You mention the pressure did not halve. I'll note that if gas production ceases with peak pressure and if the volume has doubled after the peak, then the pressure should not be about 1/2 the peak, but instead should be around 40% of the peak.

When gases expand against a piston, they are doing work against it and transferring energy to it. This energy transfer causes pressure to drop faster than application of the basic gas law would suggest, which is the halving you mention. Instead, the pressure drops roughly according to this formula:



where k is about 1.25 for propellant gases. For a doubling of volume, this represents about a 60% drop in pressure. Further, heat losses to the barrel and chamber accelerate this ideal pressure drop.

This is why I've been harping about the shape of all the pressure traces; they simply do not fall fast enough after peak pressure. Instead, they are well rounded near the peak pressure.

I found no suitable high pressure traces on the RSI page. The 7 STW plot there is interesting but suspect. The shape of the pressure curve (excluding the spike) demonstrates QL's limitations. Using the two available Nosler bullet weights and looking at several powders, I cannot get a pressure trace from QL that has the very slow fall off in pressure recorded nor the (astounding) indicated muzzle pressure. With the slowest ball powders, QL is predicting burning with the bullet well down the barrel.

PRM, I had a 23" std. chamber 338/06, read LOTS of articles on the round by Finn Aaggard, Steve Timm, and others. The consensus showed IMR4320 to do very well.

Mine shot 2909 w/200s, 2790 w/215s and 2670 w/225s. IMR4320 shot top speeds and accuracy for me and I don't think much more could be gained and stuck with it, 1/2 MOA was norm in the Hart tube- a hvy sporter. RL17 might be just right, but I'd be 4350 would be better with the 250 and up class. If you want to try another powder and perhaps pick up a tad speed if needed, you might try 4320.

A 21" tube might cost you 30-50 fps IMO over the 23 I had which is moot. FWIW, I used WW brass, partial sized, std. primers. My throat was long, done for 250s, so my OAL was out there, maybe helping case capacity.

Your goal should be in reach safely IMO.

In trying to learn when burn-out occurs relative to peak pressure, I've gone through the limited materials readily available here. The best reference at the local library is Corner's book. This was written in the UK just after the war to summarize the state of the art with regards to theoretical calculations. Digital calculations of the formulas used was just beginning and not greatly covered; at that time "computer" was generally a person's title, not a machine.

Results of simplified burning models were poor. These assumed burn-out occured near peak pressure, and they showed the fast fall off in pressure I've been noting, which does not match the rounded fall off his piezo data shows. Interesting are his comments on how burning in guns differs from that in pressure vessels due to erosive effects on the charge of the gas flow.

As the math models become more involved, the theoretical calculations begin to better match piezo data and the burn-out moves to after peak pressure. Confounding their calculations was the engraving of the projectiles into the barrel, a problem which confounds the calculations in sporting rifles to this day. Of note was that burn-out could in principle occur after the muzzle.

While quite interesting, Corner's work does not answer the question I raised. Corner was concerned with "guns" which are cannons and howitzers. He favorite example was a hefty AA gun. The propellants were not progressive; the engraving forces were relatively small; the loading densities were lower than in sporting rifles; and the chamber volumes were huge compared to the bore cross section.

It'll be months before I can get some time at the big engineering library down the road. I remember there is a book there by Krier with a section on the simulation of small arms circa 1970, and perhaps some answers might be found there. I do recall that bullet engraving was a problem on the models, but perhaps there will be some relevant experimental results.

Karl

I have done a little testing in a 270, 30-06, 338 all of which performed best with slow burning powders in any given barrel length...I did this many years ago because the general concenses was that fast burning powders got more velocity in short barrels because the supposedly burned all the powder..For what its worth most of the early gun scribes promoted this therory in most of the magazines as I recall...

I tried it and I didn't get the same results they did, I was stringhaulter and gilflurted for my opinnion! ..I don't know how some of this stuff gets started, its like some expert makes a wild claim and the whole world just excepts it because of who said it, but hey thats how we got our last president isn't it...:)

You still cooking menudo , Atkinson ? Had a bowl of the really good stuff in Lamesa last week .

All I know about the current topic is what I done and what happened as a result :

I got a 300 ultra ,then a 338 Ultra in 700 Remmies as soon as they came out . I settled on RL 22 like most everybody else at that time . RL 25 wouldn't get close to the same velocity . These were both factory rifles with 26 in barrels .

Then I had a 7 Ultra made on a Ruger No. 1 leaving the barrel at 29 i/2 in. Believing the same stuff you and I read , I tried the RL 25 since I had a longer barrel to work with .

Sure enough , I got higher velocities with the RL 25 than with RL 22 . In fact I got much higher velocities than the books showed and more than would usually be attributed just to more barrel length .

That brings me to the question I came here to ask : If all the powder is burned , and the gas can't keep up with the bullet , how come longer barrels shoot faster ?

Just kidding . I know why .

You have a major uncontrolled variable in your comparison of 22 or 25 working better in different length barrels: you changed the cartridge when you built the long barreled gun. Going to a smaller bore on the same size case is pretty much the recipe for needing a slower powder to get better velocity.

Not to argue , but , 7828 works best in my 257 and 270 wby's. Then the 7 rem mag likes RL 22 which is faster .

And everybody knows the " double radiused shoulder " is just an advertising gimmick - Right ?

I'm getting the impression we're not on the same page.

I'm not saying that two different cartridges, even of similar capacity and performance potential, can't like different powders best.

What I am saying is that a particular cartridge, 7mm Rem. magnum for example, that finds RL22 to be a clear winner in a 26" barrel isn't going to suddenly like 4064 the best if you have that same barrel cut and crowned to 20" for some reason.

Sorry , I might shoulda ' 'splained that I was addressing the second sentence in your post .The three cartridges I mentioned are the same case with three different bore sizes .

Your statement is true when dropping from .284 to .277 . Not true from .277 down to .257 . At least in my rifles .

And , the 300 and 338 ultras like the same powder . Granted , those cases ain't exactly the same .

This just proves that when anybody posts a " truism " , some bonehead will try and point out an exception .

You still aren't getting my point.

Your post read as if when you went from 26" to 29" barrels was when RL25 took over because the slower powder did better in the longer barrel. As if you could lengthen the barrel on the 300 or 338 and then 25 would take over from 22.

My contention is it was more likely that you reached the tipping point of needing a slower powder when you went from 300/338 to 7mm on the same class case. In the 7mm on that case 25 would be faster in a 29" or 26" or 23" for that matter.

"As far as I've been able to determine (and I'll say it yet again), the end of effective burning is signalled by the pressure peak."

Is ALL of the powder that is going to burn burned at the at the pressure peak?

The reason I ask, as the bullet accelerates down the barrel,the bore volume is increasing, resulting in a corresponding drop in pressure.

If the bullet is out running the pressure build up of powder continuing to burn, would not that also result in the pressure drop.

I remember reading that for the M1 Garand, a powder in the burning rate range of IMR 4895 is recommended over a slower powder such as IMR 4350. The reason given is that the pressure, with IMR 4350, at the gas port opening, is too high and can cause damage to the gas operated mechanism, where the pressure from the smaller amount and faster burning rate of IMR 4895 has dropped low enough to prevent damage to the operating rod.

This would indicate to me that a larger amount of slower burning powder remains at a higher pressure, even after the peak has been reached, for the entire length of the barrel.

The peak would not necessarily be higher or last for a longer interval, but the drop in pressure on down the barrel would not decrease as much.

No, all it means is that the volume of gas is greater with the larger charge of IMR4350, which cause pressure to be higher down the barrel, all the way to the muzzle.

Volume can't be more. The volume of the bore stays the same regardless of powder used, although the volume increases as the bullet moves down the barrel.

At, for example, 55,000 PSI, the compression of the gas in the barrel would be the same with either powder, but since the larger amount of 4350 produced more gas (and is possibly still producing) the pressure on down the barrel does not decrease as rapidly as the volume increases as the bullet moves forward, increasing the bore volume as it travels.

However, this theory comes apart if you consider that the peak pressure of 55,000 PSI for either 4895 or 4350 remains at 55,000 for the same interval.

1234567, there are two factors raising the pressure at the gas port. First, there is simply more gas due to the larger charge. Second, in order to avoid excessive pressures early on, this gas has to be created later in the bullet's travel. Since the total volume behind the bullet at the gas port stays the same, this means the gases in the bigger (slower) charge didn't have as much expansion. Less expansion means less energy transfer to the bullet, leaving more energy in the gases. In short, more units of gases with each unit of gas retaining more energy.

I've checked over numerous reports available at army lab web sites. Unfortunately, the older papers most likely to answer whether all the propellant is burned by the peak pressure point aren't (yet) available digitally.

Recent reports show the army is actively trying to improve the modeling of small arms ammunition. The biggest inaccuracies come from primer ignition and bullet engraving, and work is being done on both these fronts. One abstract suggested the army isn't entirely satisified with the performance of the 5.56 NATO and wants to get more fps out of it. Frontal ignition is being studied again.

In conjunction, the army is working on full 3-D modeling of the flows inside both guns and small arms.

Reports from the 1980s summarize what could already be done using their lumped parameter modeling. Work in this field is still quite active with the army labs. Such models are extensions of those summarized by Corner in the late 1940s. QuickLoad is such a model, but it uses a different burning model. In these older reports, cannons were calculated to have burned as little as 30% of their charge when peak pressure was reached, and signficant burning was calculated as the muzzle was approached. Sadly, no small arms examples were included.

I'll keep looking for a definitive answer. I remain convinced a fair portion of the charge in a rifle burns after peak pressure.

Karl

I'll be very interested in what you find.

By the way, your answer on the Garand 4895/4350 is correct as I understand it. The max charge with a 150-grain bullet is around 50 grains with a 150, while it's about 60 grains with 4350. This means 20% more gas in the same bore volume, which means the slower powder maintains higher pressure further down the bore..

MD , In your illustration , is the speed of the bullet as it exits the muzzle the same with either the fast or slow powder ?

Learned a lot reading this thread, hope there's some more research coming from 2525.

"I remain convinced a fair portion of the charge in a rifle burns after peak pressure."

I think I agree, but the point is academic. It is moot practically, ie: if peak pressure is around 3", even if powder finishes burning at 6"....

Or are you saying powder could still be burning at 16" ?

Man Oh Man!

How can you guys have 6 pages of this conversation without mentioning the new Hodgdon Superformance powders?!

The whole proposition that Superformance is based on is that powder doesn't completely burn in the barrel!

If you read nothing else, read the first paragraph of this document:
Superformance Technology

Easy, it wasn't out when this thread started. I do have some Leverevolution powder on the way though. Hope to shoot in the next few weeks.

LOL! I didn't notice that! Boy, this was dredged up from the bottom of the pile!