Barrel length and powder burn rates?

[AJ Peacock]

SU37,

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.


AJ

 

[bookworm]

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

 

[338 LEGEND]

Is there somthing wrong with the last 4" of the barrel? hope your not cutting off good barrel. are you ?

 

[bookworm]

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 accuracy...in 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.

 

[338 LEGEND]

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.

 

[Ridge Runner]

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?
RR

 

[su37]

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."

 

[Ridge Runner]

what part of
I have dumped unburnt powder out of cases when fired from a 12.75" barrelled pistol
I have dumped unburnt powder out of cases when fired from a 12.75" barrelled pistol
I have dumped unburnt powder out of cases when fired from a 12.75" barrelled pistol
I have dumped unburnt powder out of cases when fired from a 12.75" barrelled pistol don't you understand? wanna act like an idiot? cool I'll deal with it.

I'm not a ballistics whiz, nor a reloading guru, but I know this.
When shooting IMR 4350 in my rifles I've never saw this, never saw it with any other powder, but I have dumped unburnt IMR 4350 out of the cases of my 7mm JDJ. say what you want, I have burnt hundreds of pounds of powder and never saw that tiny bit of unburnt powder until I loaded the 7 JDJ up with 4350, there would remain in the case 7-8 "kernals" of powder, half of which were white and looked to be just ash, the rest were powder which was slightly discolored but not burnt.
Now take your know it all attitude and put it where the sun don't shine cause I ain't buyin it!
RR

 

[su37]

Now take your attitude punk and learn how to read the whole post and just see what i did say.

"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.



All I did was offer a view point that did not agree with the common wives tale that powder burns all the way down the barrel.
It does not!

If you don't agree I could care less.

 

[Ridge Runner]

punk huh, whatever, you've shown us what you know about things

You've shown a new "view" as you put it, which doesn't correspond with what folks see when they shoot in the real world, ummm! where do you shoot?

If its a wives tale just explain why a longer barrel gets more velocity?
and explain why I have unburned powder in my 7mm JDJ cases? and I'm thinking that 1% of 43 grains isn't 7-8 kernels of powder.

So mr knows everything why isn't there that 1% in the cases of my 270 weatherby, 25 wssm, 7mm STW, 7mm AM, 7mm RM, 6.5 Gibbs, 6mm rem, 6 ppc, and the rest, only the 7mm JDJ shooting IMR 4350?

BTW I hope we meet one day so you can call me a punk face to face, until then, have a good day!
RR

 

[su37]

If there is a mr. know it all it's you bud. I disagree and people here get the panties in a wad.
I took the good natured ribbing here from others with a good LOL.

So what's your problem butter cup?


Your question, "If its a wives tale just explain why a longer barrel gets more velocity? "

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

Don't you know how to comprehend? I have already stated this in a past post.


The ole' adage that you use fast powder in short barrels and slow powder in long barrels
is bogus. You can use slow powders in short barrels. Of course your speed will be down as a result, no arguing that.

 

[AJ Peacock]

If there is a mr. know it all it's you bud. I disagree and people here get the panties in a wad.
I took the good natured ribbing here from others with a good LOL.

So what's your problem butter cup?


Your question, "If its a wives tale just explain why a longer barrel gets more velocity? "

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

Yes, as the bullet goes down the barrel, the gas has to expand. The pressure will drop. This is known as Boyles law. Boyles law is a special case of the ideal gas law that deals with systems that have a constant temperature. Now, in your universe, the powder is all burnt, so the temperature has to be dropping; check the Ideal Gas Law, this lowering of the temperature will also cause a drop in pressure. Without decreasing the volume (can't happen as the bullet progresses down the barrel) or increasing the temperature (can't happen in your world, as the powder is all burnt already) or increasing the amount of gas (can't happen in your world if the powder is all burnt), the pressure has to precipitously drop as the volume increases. According to your supposition, long barrels would tend to slow a bullet down. A 22LR will slow down after about 16" of barrel length due to this affect. We use slower powders to keep this from happening in our centerfire rifles.

If however, something other than the Ideal Gas Law is working AFTER the powder is burnt, please let us know. The law is only about 400yrs old, so maybe it hasn't been fully investigated and is actually incorrect.

Don't you know how to comprehend? I have already stated this in a past post.


The ole' adage that you use fast powder in short barrels and slow powder in long barrels
is bogus. You can use slow powders in short barrels. Of course your speed will be down as a result, no arguing that.

Enlighten us with the calibers you are reloading with slow powders and short barrels. Let us know how it is working for you. If the powder is all burnt, why are you loosing speed? Wouldn't fast and slow powders work the same, regardless of which powder you use in a short barrel?

You can't have it both ways, either the powder is burnt and should all work the same, or it isn't burnt and that is why you are loosing velocity (and this argument )


Unless, you agree with #1 on my previous post. If this is the case, then let us know. You never responded to my question, trying to clarify your position.

Thanks,
AJ

 

[steve smith]

OK Su37, Lets go back to high school chemistry class.

So lets take 5grams of fuel and 5 grams of O2, initiate combustion. The end result is you will have 10grams of gasses. So with smokeless powder the fuel and O2 are tied together in a chemical bond that is broken and then rearranged, resulting in the release of energy in the form of heat and the conversion of the solid to gas.

State 1- solid fuel+oxy (atmospheric O2 doesn't have any effect)
State 2- combustion products in the form of gasses (with solid residue being negligible).

Now for all intended purposes, the density of the gasses (whether from single base or double base, slow or fast burn rate) is identical. So, from this we can infer that whatever powder your using each powder will produce the exact same volume of gasses grain for grain. 5 grains of powder will produce 5grains of gasses at a volume of .xxx m^3.

So, from that we see that the only way to keep a load of 52gr of powder A (Ramshot Enforcer) and a load of 102.5gr of powder B (WC-872) , at the same maximum pressure is to slow the rate of deflagration. Both powders being double base ball powders in an extreme comparison in my 270-300Rum using the same bullet, pushed to max pressures.

Now, if we take powder A, your assertion that all the powder has completed combustion by the time the projectile has moved a few inches in the barrel could be correct, but in the case of powder B your assertion would make allmost 2x the amount of gas fit into virtually the same volume as in the case with powder A, yet still only have the same pressure. This simply cannot happen!

Now, your statement about "The gas created keeps expanding" is correct, but unless someone has been able to slow the rate at which gasses expand without the pressure going thru the roof, this is not what's going on. At least not entirely. What is happening is the rate of gas generation is much slower. In other words combustion with powder B continues long after combustion of powder A has completed. Now when I say "long after", it's really only about a ms, but when your talking bullets traveling down the barrel it's the difference between combustion completing at 2" vs 30".

Now then, If you don't believe that or don't understand it, then like before I suggest you go take a chemistry class and more especially a thermodynamics class. I promise you that it would really open up your eyes up to what wives tales you believe to be fact.

 

[justgoto]

Lol!:d