Barrel Length Needed to Burn Up Powder?

[Southern Shooter]

Is there information out there that tells how much barrel length is needed to more completely burn up certain powders?

More specifically, I am interested in how much barrel length is needed to burn up:

.45 caliber
315 grain bullet

H110/W296 @ 29 grains
IMR 4227 @ 29 grains

[ejcrist]

That's a great question I've had for a long time too. I remember reading somewhere that it doesn't take much barrel length to get a full burn, and that the longer lengths benefit from slower powders because they maintain pressure behind the boolit longer. I know that's not a very scientific answer but it seems to be true from my own personal experience. I've had a couple of 4 5/8" barreled revolvers (32 H&R and 38 Spl) that shot extremely well with Bullseye whereas all my longer barreled revolvers shoot best with 2400, H110, and IMR 4227.

[yovinny]

Wouldent that depend on quantity and containment (caliber/case capacity) ?

[Southern Shooter]

Original post edited

[BossMaverick]

Are you talking a complete burn of the flakes or granules, or a burn in which gases are not being absolutely produced anymore? If the latter, a complete burn could be achieved by using a very fast burning powder in a pistol caliber carbine. My preferred .45acp load uses Solo 1000 (a fast burning single based flake powder). You have to be shooting at night with my handguns to see any sort of muzzle flash (and even then, you have to be carefully watching for it). If I shot the same load in a .45acp carbine, there would no doubts the powder would be completely burned off and the extended barrel length would actually be reducing the velocity due to friction. I would guess the burning would be complete by 8" of barrel length (but again, that is just a guess).

With that being said, the practical answer is that the effective burning is over in the first couple inches of the barrel (in handgun calibers at least). The majority of the velocity is produced in that length and the pressure starts falling from the bullet traveling down the barrel, which increases the volume for the powder's gases. After that length, increase in velocity isn't as extreme and becomes more gradual.

Please forgive me if linking to outside sources isn't allowed, but the Western Powders blog has some interesting articles on ballistics. Here is a relevant article: http://blog.westernpowders.com/2014/11/powder-choice-and-carbine-performance/

Edited to Add: I see you edited your post and removed the "Dot" powders. The slower powders make the answer more mystical, but the super-effective burn is still over in the first few inches. You will still have to experiment to make sure you aren't using too slow of a powder (which is evident by seeing unburned granules or having very dirty burning).

[Southern Shooter]

Thanks for the info, thus far.

What I am trying to do is get the most efficient use of whatever powder used ( in my case, H110/W296 and IMR 4227 ) and the gases it produces with a .45 caliber 315 grain checked cast boolit in a 16" barrel rifle.

[country gent]

I have seen some tests in magazines where a long barrel was fitted and shot for velocities and cut back in 1" increments and re fired with the same loads till velocity started dropping off. Cant remeber which magazine it was in though.

[762 shooter]

I thought Quickload did that.

762

[BossMaverick]

Thanks for the info, thus far.

What I am trying to do is get the most efficient use of whatever powder used ( in my case, H110/W296 and IMR 4227 ) and the gases it produces with a .45 caliber 315 grain checked cast boolit in a 16" barrel rifle.

It helps to know the cartridge so we can look up the specs. Case volume and SAAMI pressure specs does make a difference. A .45 caliber bullet loaded into a necked down .50bmg case with 20gr of 4227 will produce a very low pressure round while a .45 bullet loaded into a .45acp case with 20gr of 4227 will produce disastrous pressures.

I went to the Hodgdon website to try to figure out the cartridge to know what the suggested powders are. I'm assuming you're loading .45 Colt (hot load specs), .454 Casull, or the like. The powders you mentioned are suggested powders, so you shouldn't have to be worrying about not getting a complete burn, especially in a 16" barrel. Considering those cartridges and loads are hot rounds in a pistol with a lot of expelled gas once the bullet leaves the bore, you are probably getting fairly efficient use out of the powders in the 16" barrel.

Unfortunately, you won't ever find data to know the exact barrel length for when the burn is complete. There are just too many variables (case volume, powder burn rate, primer effectiveness, bullet composition, bullet weight, barrel friction, etc). Even if the burn was completely done at 10", there is still a high enough PSI from the remaining gases in your loads to keep the bullet velocity increasing. Think of it like a potato gun using a chamber of compressed air. There is no burning at all but the PSI from the compressed air keeps the potato accelerating until it leaves the barrel. Trying to reduce the powder charge or changing to a faster powder to end the burning sooner will reduce the final velocity. Trying to go to a slower powder to end the burning right as the bullet leaves the bore could result in an overly high pressure round, or at the very least, a louder and flashier round.

[BossMaverick]

I have seen some tests in magazines where a long barrel was fitted and shot for velocities and cut back in 1" increments and re fired with the same loads till velocity started dropping off. Cant remeber which magazine it was in though.

That may be a way to determine that one load's acceleration characteristics, but that will be just for that single load. Do something as simple as changing the powder charge, powder type, or bullet weight will completely change the characteristics. Change the cartridge and you can toss everything out the window.

The link I posted shows just how powder burn rates and charges will completely change things.

[Southern Shooter]

Good point, BossMaverick.

.454 Casull

[Sensai]

I thought Quickload did that.

762
It does.

[JohnH]

Are you talking a complete burn of the flakes or granules, or a burn in which gases are not being absolutely produced anymore? If the latter, a complete burn could be achieved by using a very fast burning powder in a pistol caliber carbine. My preferred .45acp load uses Solo 1000 (a fast burning single based flake powder). You have to be shooting at night with my handguns to see any sort of muzzle flash (and even then, you have to be carefully watching for it). If I shot the same load in a .45acp carbine, there would no doubts the powder would be completely burned off and the extended barrel length would actually be reducing the velocity due to friction. I would guess the burning would be complete by 8" of barrel length (but again, that is just a guess).

With that being said, the practical answer is that the effective burning is over in the first couple inches of the barrel (in handgun calibers at least). The majority of the velocity is produced in that length and the pressure starts falling from the bullet traveling down the barrel, which increases the volume for the powder's gases. After that length, increase in velocity isn't as extreme and becomes more gradual.

Please forgive me if linking to outside sources isn't allowed, but the Western Powders blog has some interesting articles on ballistics. Here is a relevant article: http://blog.westernpowders.com/2014/11/powder-choice-and-carbine-performance/

Edited to Add: I see you edited your post and removed the "Dot" powders. The slower powders make the answer more mystical, but the super-effective burn is still over in the first few inches. You will still have to experiment to make sure you aren't using too slow of a powder (which is evident by seeing unburned granules or having very dirty burning).

An excellent read. Handguns don't show the difference nearly as much as rifle cartridges and rifle length barrels do. A look at data from the Lyman 49th edition shows a very nice correlation between what is a very fast powder for the cartridge, Unique; and a powder that is a near perfect speed for the cartridge, IMR 4320. A max charge of the Unique, 24 grains, with Lyman #311672 a 160 grain cast boolit makes 2182 FPS at a pressure of 56,700 psi. The IMR 4320 driving a Nosler 165 grain Ballistic Tip with a max charge of 52 grains makes a velocity of 2843 PSI at a pressure of 57,500. It's really all about gas volume. As well, most powder composition involves about 20% of actual nitrocellulose/nitroglycerin coumpound. The balance (80%) of the powder is burn deterrents and plasticizers. The nitrocellulose/nitroglycerin compound is consumed within the fist couple inches of the barrel. All that flash at the end of the barrel is the "garbage" of the powder; all the component stabilzers, burn deterrents, plasticizers which are needed to make the powder but add nothing to actual "bang".

[NavyVet1959]

I remember reading somewhere that most powders have about the same amount of energy on a per pound basis, but due to grain size, burn deterrents, etc, they release that energy over different amounts of time. Also, higher cartridge pressures can affect the burn rate.

Let's say that you start out with a bullet loaded over a 1" chamber and you instantaneously introduce 50,000 psi to it and no additional gas is being produced. As the bullet travels down the barrel, your gas chamber is increasing and you have the pressure decreasing as such:

50,000 psi w/ 1" chamber
25,000 psi w/ 2" chamber
12,500 psi w/ 4" chamber
6,250 psi w/8" chamber
3,125 psi w/16" chamber
1,562.5 psi w/32" chamber

At some point, the pressure in the barrel is no longer sufficient to keep accelerating the bullet moving down the barrel given the resistance of the barrel to the lead. This resistance is affected by various things -- the friction of moving lead down the barrel, the depth of the rifling, the harness of the lead, etc. At that point, increases in barrel length will result in decreases in the velocity of the bullet as it leaves the barrel. Of course, this is assuming a completely closed system where no gas can escape back around the cartridge case and the bullet fully seals the bore. An instantaneous pressure system like this will have the greatest acceleration initially and then it will taper off as the projectile travels down the barrel and the pressure behind it decreases. The velocity of the projectile might be increasing, the the acceleration might be decreasing. Acceleration is the first derivative of velocity.

But powders don't generate pressure instantaneously. They burn, creating gasses. Various things make them burn faster or slower. All the grains of the powder don't start burning at the same time. The primer might start some of grains burning, which then start other grains burning, which then start other grains burning, and so on and so on... Because of this, it's entirely possible to have two powders that generate quite a bit of difference in their initial peak pressure, but result in the same muzzle velocity.

I think the end result of this is that there is no easy equation to be able to calculate this out -- way too many variables and many are not even related to the actual powder. The best you can hope for is to do a lot of experimentation and get data for your particular firearms, bullets, alloys. If you don't have a piezo pressure test system though, in the end, you're probably just guessing. :(

Now, if you were actually able to come up with equations that could work for this, I suspect that for at least a couple of fields, it would be applicable for a graduate level thesis paper.