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Barrel length and powder burn rates?

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Unread 06-05-2009, 11:53 AM
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Join Date: Oct 2005
Location: Michigan
Posts: 2,232
Re: Barrel length and powder burn rates?


In looking through my reference library to try and prove 'your' supposition, I happened upon a couple paragraphs from Julian S. Hatcher, whom certainly should need no introduction.

From pages 309-312 of "Hatchers Notebook" (pages 310-311 are pictures only), he discusses burning rates and methods to slow burning to extend the pressure as the bullet proceeds down the barrel. The following is quoted, any typos are certainly mine. I've highlighted portions that are directly relevant to our discussion.

" The great trouble with getting high velocity in a gun is the fact that when the powder in the cartridge is ignited it turns into gas, and this gas, confined in the small space of the cartridge case, creates a very high pressure which pushes the bullet along the bore of the gun. But as soon as the bullet starts to move along the bore, that leaves more space for the gas to occupy, hence there is less pressure, and the effect of the powder will rapidly fall off to nothing unless special means are taken to keep the pressure up.

One of these special means is the perforation of the powder grain, which causes it to have a larger burning surface as the combustion proceeds. This is because the primer flash ignites the inside of the tube as well as the outside of the grain. As the grain burns, the outside surface gets smaller, hence the rate of evolution of gas would burn away, and the diameter of the hole becomes larger, with a corresponding increase in the interior burning surface.

The balance between these two surfaces can be controlled by the ratio of the inside diameter to the outside diameter in the finished grain of powder. In cannon powders with their larger grains, there are usually seven perforations instead of one.

Another method of controlling the burning of the powder and making it more progressive, that is, making it holdup its pressure longer during the travel of the bullet, is by coating the powder with a substance which makes it burn slowly at first. As this coating burns off the outside of the powder, the speed of combustion increases. These progressive-burning powders tend to give a more uniformly distributed pressure, sustained longer during the travel of the bullet. Moreover, the maximum pressure is not so high because instead of being exerted all at once, the pressure is spread out more evenly during the entire travel of the bullet. The du Pont "Improved Military Rifle" powders such as I. M. R. No 3031, I. M. R. No. 4320 and I. M. R. No. 4064 are progressive powders.

Like black powder, smokeless powders are also controlled as to their speed of burning by the grain size. Powders with very fine grains burn up in a hurry and therefore are particularly suited for short-barrel weapons. Powders with very large grains take longer to burn up, and are adapted to long-barrel weapons such as cannon. ..."

The text continues to talk about granule size and ignition dynamics, but is not directly relevant to our current discussion.

I'll sit here on the same page as Julian S. Hatcher, I also suspect that Powley is sitting here beside us.

If some is good and more is better, then too much is just right.

My mind is a raging torrent, flooded with rivulets of thought, cascading into a waterfall of creative alternatives
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Unread 06-06-2009, 10:45 PM
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Join Date: Dec 2008
Location: SW Idaho
Posts: 193
Re: Barrel length and powder burn rates?

Well, I never thought my initial question would have sparked 7 pages of discussion. It was very informative to say the least - I learned a lot!

I think the bottom line for me is that I will keep my 26" barrel and H-1000 powder for now. If I get the accuracy I need out of that combo that is worth more than the little bit of mobility I might gain from a shorter barrel.

I wish I had the luxury of testing multiple barrel lengths with various powders to put some of these ideas through their paces. Sounds kinda fun.

In the mean time, if anyone has first hand experience (good or bad) with the combination I originally asked about, I'd be interested in your thoughts.

300 win mag
20" - 24" barrel
Slow powder (H-1000)
190gr match grade bullet
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Unread 06-07-2009, 12:57 AM
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Join Date: Jan 2009
Posts: 196
Re: Barrel length and powder burn rates?

Is there somthing wrong with the last 4" of the barrel? hope your not cutting off good barrel. are you ?
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Unread 06-07-2009, 02:52 PM
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Join Date: Dec 2008
Location: SW Idaho
Posts: 193
Re: Barrel length and powder burn rates?

Well actually there is nothing wrong with the last 4" of my barrel that I know of. I'm certainly not planning to do anything hasty, but I am/was exploring the idea of going with a shorter barrel.

I've read some articles that say the shorter length can buy you some stiffness and in turn some many cases at the expense of some velocity.

The shorter barrel is also appealing from a packability standpoint.

My plan at this point is to get a new stock (probably HS precision) and adjust the trigger a bit lighter and see where that puts me accuracy-wise.

I am actually pleasantly suprised with the accuracy out of the box on this rifle. With match ammo my best 5-shot group was 0.9" and my worst 5-shot group was 1.3". That seemed pretty good to me, but I'm hoping to get a bit better. I'd like to average sub-moa and am hoping that the stock and trigger will do the trick. If it does then I likely won't touch the barrel.
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Unread 06-07-2009, 04:10 PM
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Join Date: Jan 2009
Posts: 196
Re: Barrel length and powder burn rates?

Sounds like you have a good gun, I have reloaded for the 300WM for 20years its a wonderful hunting round and is a very good long range performer. Reducing the barrel lenght will take away its full capacity. 26" is a good lenght for the 300, my 300 has a 27 1/4" barrel and shoots lights out I think I would do every thing I could before cutting off the barrel. To me a 22" 300WM is a waist, your looking at 30/06 velocity.
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Unread 06-07-2009, 04:59 PM
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Join Date: Dec 2002
Location: mathias wv
Posts: 987
Re: Barrel length and powder burn rates?

Originally Posted by su37 View Post
Differ burn rates create or develop differ pressure curves.

It's the pressure that remains in a longer barrel to give the bullet more velocity not continues burning powder.

Slow powders in short barrels actually works very good contrary to popular gun belief.
SU, regardless of what you think, I cannot agree with your line of thinking about powder burn rates, this is due to what I have saw in the past in my own experiences.

I have dumped unburnt powder out of cases when fired from a 12.75" barrelled pistol so to me that blows the "all powder is burnt in 2" deal out of the water.
if it was all burnt in 2" then a 30" barrel would be slower than a 24" is that not correct?
Born to Hunt, Forced to Work!
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Unread 06-07-2009, 05:55 PM
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Join Date: Jan 2006
Posts: 364
Re: Barrel length and powder burn rates?

I'll repeat for the last time what was stated and what is obvious.

"Even at the correct pressure a tiny bit of powder doesn't burn, 1% or less. But again, it simply isn't going to burn. All the powder that WILL burn is burned up just in front of the chamber.

So no, different powders don't ALL burn up within the exact same distance in front of the case. The cartridge, powder, bullet all have an effect, and the point of peak pressure does vary. But the powder doesn't keep burning on down the bore. The gas created keeps expanding."

"But the powder doesn't keep burning on down the bore. The gas created keeps expanding."

"But the powder doesn't keep burning on down the bore. The gas created keeps expanding."

"But the powder doesn't keep burning on down the bore. The gas created keeps expanding."
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