Powder burn rate and barrel length

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Zendude

Zendude

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Would it be better to choose a faster burning powders for short barrel pistols to avoid the bullet exiting the barrel before all the powder is burned? Or is the burn rate of slow burning powders still fast enough to finish burning by the time the bullet exits a 2 inch barrel?
 
The flash at the end of the barrel isn't powder that hasn't burn yet. It is the gasses created from the powder igniting. A large percentage of powder is burned inside the first 4-6 inches of barrel. Hence why some cartridges use the sa me powder in rifle or handgun. If the power is all burned in a 6 inch handgun it is gone in a 22-26 rifle barrel.
 
Medium burn rate powders will give you all you can get out of a 2" barrel.

And More then you can get with faster powders.

Even slower Magnum class powders will exceed medium burn powders.
At the expense of horrendous flash & blast from residual bore pressure.
Not from unburned powder though.

rc
 
Slower powders.

Whatever gives the fastest in long barrels will do the same in short barrels.

As rc mentions you also get a a lot of blast and flash.
 
Good question and I look forward to reading input on this one. I went through much the same with a rifle and I no longer try to use the fastest powder I can get away with, but the slowest powder I can get away with, muzzle upset notwithstanding.
 
In my limited experience beyond commonly published loads I got my best full power .38 snubbie HBWC velocities in the following order:

Blue Dot
Unique
Red Dot
Bullseye

In my Raven .25 using 35gr Gold Dots

Unique
Red Dot
Bullseye

Not what I expected based on conventional theory, but I too believe that when velocity is the goal, use the slowest that still works, and at the highest charge within acceptable limits.
 
I'm having a hard time w/ this guys.

All powders, fast or slow, have a specific energy released per grain burned

You want the powder that releases the maximum total energy (Pressure X Distance)...
- In the length of barrel available for release... (The Distance)
- Within the pressure limits of the weapon (The Pressure)
(In other words, integtrate the area under the pressure/bullet travel distance curve)

There ain't no free lunch:
Pressure builds slowly with slow burners but sustains over a longer distance.
Pressure builds faster with fast burners buts drops off quickly with distance.

If slow burners provide you that max sustained pressure over that short barrel distance, you have a winner -- regardless of how much unburned powder you dump out of the end of the barrel after the bullet leaves the muzzle.

BTW: Someone's going to have to explain to me how all powder fast-or-slow actually burns
when the resultant barrel remains filled with -- and the front of the bench is covered with --
unburned powder grains,

-
 
It's not unburned powder you are seeing. It is actaully a form of ash that is created. Sometimes you can take a brass case and dump it out after firing. You will see that even though it looks like kernels it won't ignite. There are much smarter ppl than I that have shown and proven that the muzzle blast is from gases. Slow motion video also shows that there isn't unburned powder. I use to think the same thing when I saw kernels falling out of my revolver.
 
Powder skeletons, as they are referred to, are a by product. Some powders and cartridge combination may produce a more noticeable amount, but I assure you it's not powder.

I've had two occasions in which I actually did get unburned powder, quite a bit actually. Both occurred the result of using a standard primer where a magnum primer was specified in the data. Once with H110 with CCI-500's, and once with a really heavy charge of RL22 and CCI-200's in 7mm RM with 100 gr. varmint HP's. In those circumstances the unburned powder, was truly unburned.

GS
 
BTW: Someone's going to have to explain to me how all powder fast-or-slow actually burns
when the resultant barrel remains filled with -- and the front of the bench is covered with --
unburned powder grains,
Click to expand...

I doubt anybody can expalin all of it, because powder burn rate is not a simple matter of one powder burns at one speed, while another powder burns at another speed. I doubt any powder burns at the same speed throughout the burn cycle. Most powders burn faster as they get hotter, and as presure increases. For example, the condition your describe of unburned powder might often be rectified by INCREASING the powder charge in many cases to increase pressure and accelerate burn. You have to think of a powder's burn rate as a curve that shows changes as its conditions during the burn cycle changes, and a single plot of a graph. If you're a mechanical guy, think of it as being like a motor's horsepower chnaging with rpms.
 
Ccctennis said:
It's not unburned powder you are seeing. It is actaully a form of ash that is created. Sometimes you can take a brass case and dump it out after firing. You will see that even though it looks like kernels it won't ignite. There are much smarter ppl than I that have shown and proven that the muzzle blast is from gases. Slow motion video also shows that there isn't unburned powder. I use to think the same thing when I saw kernels falling out of my revolver.
Click to expand...


That clears that question up. I thought it was unburned powder too. When using Remington UMC ammo in my 380, it looked like sparks would shoot from the muzzle and the ejection port. I thought it might have been from powder that was still burning.
 
MEHavey said:
I'm having a hard time w/ this guys.



All powders, fast or slow, have a specific energy released per grain burned



You want the powder that releases the maximum total energy (Pressure X Distance)...

- In the length of barrel available for release... (The Distance)

- Within the pressure limits of the weapon (The Pressure)

(In other words, integtrate the area under the pressure/bullet travel distance curve)



There ain't no free lunch:

Pressure builds slowly with slow burners but sustains over a longer distance.

Pressure builds faster with fast burners buts drops off quickly with distance,



-
Click to expand...


That was my initial concern - whether a short barrel allowed enough time for a slow powder to burn completely before (and thereby not achieving max pressure) the bullet exited the muzzle.
 
I took one of the load manuals (Speer or Hornady - I forget) where they had load data and velocities listed for long barrels (5" or so) and snubbies (2" I believe) and I plotted a graph for each, based on the relative burn rate of the powders, and the max velocities obtained. The vast majority of the data points were in a relatively straight line, the highest velocities were almost always from the slowest powder used. The way I plotted the graph, the line was steeper for the longer barrel, meaning there was more velocity gained by going to a slower powder, but even in the short barrel the slower powders still gave higher velocities.

There were a few outliers, and that depended a lot on which burn rate chart I referenced. There can be a lot of difference in those.
 
It has been known for about 80 years that the powder that produces the best velocity in a 26" barrel will produce the best velocity in a 10" barrel.
So, if you want max velocity in a snub nose, use the powder that produced the best velocity in the manual's test barrel.
Also, last I heard, all powder that is going to burn will burn in the first 1-2".
PV=nRT, ideally.
 
" It's settled science " :rolleyes: :neener:

Well, not quite. ;) PV=nRT=Constant only applies when no energy is being injected into the system.

As I'm fond of boundary-value problems to test theories, I did a series of internal ballistics runs with the 357 at long & short barrels -- comparing fast burners to slow. While slow burners did far better than I expected, they did not produce the fastest velocities w/ short barrels.

Next, I ran a 375&H/270gr/RL-19 to find Pmax at 1.4"/55,000psi. If PV=nRT, I'd find pressure down by half at 2.8" travel. Instead I find it at 8.2" ... so energy is still being injected/powder is still being burned.

Given all the powder might not have been burned at that 1.4", I restarted the PV=nRT game at the 5"/38,000psi. PV would say the 19,000psi point would be at 10" Instead it's at 12.3" So energy is still being injected even that far down and slightly longer.

So I'm a convert to the slow-burners do better than expected; but not to the theory that everything burns within a few inches no matter the burn speed. :)
 
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gamestalker said:
Powder skeletons, as they are referred to, are...
Click to expand...

GS - you're kidding, man. Powder skeletons? Shaking head here...

MEHavey - I agree, no free lunch, however I suspect that with slower powders (esp. compressed) we're cheating by getting more efficient propulsion from the expanding powder mass before the gases take over.
 
spitballer said:
GS - you're kidding, man. Powder skeletons? Shaking head here...
Click to expand...
Reminds me of the other day when my sister asked me about the work that I was doing developing reloads for grandpop's old .32-20 Colt Army Special.

I gave her a quick answer, but she insisted on details. Shortly thereafter she started laughing and accused me of making stuff up ... swaging, forcing cone, frosted, obturation, cerrosafe, bore casting, groove diameter ... she thought I was pulling her leg ... until I backed up and slowly & fully re-explained each term and its importance.

It reminded me that just because it may sound silly doesn't necessarily make it untrue. ;)
 
Ccctennis said:
It's not unburned powder you are seeing. It is actaully a form of ash that is created. Sometimes you can take a brass case and dump it out after firing. You will see that even though it looks like kernels it won't ignite. There are much smarter ppl than I that have shown and proven that the muzzle blast is from gases. Slow motion video also shows that there isn't unburned powder. I use to think the same thing when I saw kernels falling out of my revolver.
Click to expand...

I almost lost a bet on this ^^^^ well I did ,but the RO at our indoor range wouldn't take my money,

I was shooting right up to close and help clean up , the RO was sweeping the range in front of the shooting bays , and said "I wonder if you could load up this unburnt powder" he was joking, and I said " that's just ash , the powder is all burnt up before the bullet leaves the barrel and the flash is the gas hitting air" he said the flash is the gas hitting the air, but this unburnt powder comes out after that , I asked if he had ever tried to light it ? he said no, but go ahead and try , I asked if he wanted to put money on it , he said he wouldn't take my money ,

there was about a 2lbs pile of dirt, ash , powder? sitting there , and just incase he was right (and seemed to think he was) I scraped about a 1" high by 4" pile away and lit it , it sparked a bit at first , then took off just like fresh powder , , started slow then real fast , with bright flame and the smoke was just like I had just shot 20 rounds down range ,

sure glad I didn't light the whole pile :eek:

our indoor range is handguns and rimfire only and a lot of hand loader's , lots of 2400, W296, Bullseye, W231, AutoComp ,... with lots of long barreled 44's, 357's, full sized 45's not many 2" stubbies

next time I'll take pictures, as I didn't think there would be anything to take a picture of . :D
 
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your 375 h&h is a bottle neck cartridge, not straight neck.
Click to expand...
That is totally irrelevant to the theory of all powder -- fast or slow -- burning in the first inch or two.
All a straight-wall does is reduced 1/2 Pmax to the 7.1" point instead of 8.5"

New energy is still being injected into the combustion chamber (i.e., the barrel) all the way down its length.




savanahsdad said:
[The "ash"] then took off just like fresh powder, started slow then real fast , with bright flame
Click to expand...
Don'cha jus' hate it when data gets in the way of settled science? :rolleyes: ;)
Good show "dad" :D
 
You really need to experiment a bit. Not only powder but bullet weights and even primers. perhaps interesting, 4.2gr. N310 is giving me outstanding accuracy behind a 185gr. Nosler JHP in .45ACP (5" barrel) - go figure...
 
4.2gr. N310 is giving me outstanding accuracy behind a
185gr. Nosler JHP in .45ACP (5" barrel) - go figure...
Click to expand...
Was there (is there?) something that would make you think it wouldn't?

14,000psi/mid-800's velocity/100% burn
 
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