Thread: Myth? - shorter barrel = use faster powder?

if you take it to extreme ...or go backwards in time...or both... black powder achieved better burns with long barrels..... folks used to TUNE a load by shooting over snow,and keep reducing powder charge till no unburnt powder exited muzzle..... sort of the same as muzzle blast thing... my old 20" 270 had one heck of a muzzle blast and big ball of flame on dark with factory loads...feed it heavy projectiles,not so bad.
a faster powder that has completed its burning inside barrel wont waste energy on muzzle blast/fireball.....
slower powder needs longer barrel to complete its burning...same as black powder.... if you dont burn it all in the length of barrel you have,you may as well reduce the charge until you do,BECAUSE you wont make projectile go any faster with more powder....I BELIEVE this is the flat spot folks look for on ladder testing???
or very similar....
shotshells use a very fast burning powder and short barrels still produce horrendous fireballs,maybe the lower pressure plays part??? ...long barrels are much nicer to use and as bonus take the bang further away from your ears.

But a 'muzzle blast' according to Wikipedia is an explosive shockwave created at the muzzle of a firearm by gasses created by the burnt powder.

"In addition to the blast itself, some of the gases' energy is also released as light energy, known as a muzzle flash".

So all the powder must be burnt inside the muzzle. The muzzle blast/fireball is light from the gasses.... not burning powder.

https://en.wikipedia.org/wiki/Muzzle_blast

Originally Posted by Micky Duck

if you take it to extreme ...or go backwards in time...or both... black powder achieved better burns with long barrels..... folks used to TUNE a load by shooting over snow,and keep reducing powder charge till no unburnt powder exited muzzle..... sort of the same as muzzle blast thing... my old 20" 270 had one heck of a muzzle blast and big ball of flame on dark with factory loads...feed it heavy projectiles,not so bad.
a faster powder that has completed its burning inside barrel wont waste energy on muzzle blast/fireball.....

Issue is it procuces gas so quickly it has to stop producing as earlier meaning as the bullet travels down the barrel this means pressure drops quickly. The slower powder takes longer to reach peak pressure but by that time it has more volume to create gas in and the pressure stays higher in the later portion of the shot cycle
slower powder needs longer barrel to complete its burning...same as black powder.... if you dont burn it all in the length of barrel you have,you may as well reduce the charge until you do,BECAUSE you wont make projectile go any faster with more powder....I BELIEVE this is the flat spot folks look for on ladder testing???
or very similar....

Definitely not true. the les powder added the less efficient the powder burn due to lower pressure. Powder burns much more readily at higher pressures (higher heats). Ie running data in QL 40 grains of varget gives me a 91% powder burnt whereas 48 grains gives me 98% thsi is due to the more efficiet burn at higher pressure. This is part of why the 277 Sig Fury is so efficient (135grain 2777 at 3000fps from a 16 icnh barrel but runs at 85kpsi vs 65ish for most cases

shotshells use a very fast burning powder and short barrels still produce horrendous fireballs,maybe the lower pressure plays part??? ...long barrels are much nicer to use and as bonus take the bang further away from your ears.

.

Originally Posted by Hermitage

But a 'muzzle blast' according to Wikipedia is an explosive shockwave created at the muzzle of a firearm by gasses created by the burnt powder.

"In addition to the blast itself, some of the gases' energy is also released as light energy, known as a muzzle flash".

So all the powder must be burnt inside the muzzle. The muzzle blast/fireball is light from the gasses.... not burning powder.

https://en.wikipedia.org/wiki/Muzzle_blast

And if you had bothered to then go to the page for muzzle flash…
“ Both the blast and flash are products of the exothermic combustion of the propellant (gunpowder), and any remaining unburned powders reacting with ambient air.”

The powder that gives the most velocity in a long barrel will also likely give the most velocity in a short barrel.

Originally Posted by Hermitage

Dude, this bloody forum is going down hill because of responses like yours.
There are less and less questions being asked in this forum.....it is getting boring...really boring.
But when I do ask a genuine question I don't get a forum boosting answer, instead I get 'I can't be fucked'.

Good going...

Disagree i think its more of a cant be fucked because you give a long in depth answer and someone will just rip it apart anyway.

He is talking about quickload not a ballistic's program so right from the get go they on a different page

Back to the op

In theory yes but not always the case especially when using heavy for caliber bullets as the fast burning will pressure spike a lot sooner.
You will find barrel to barrel difference to be a big factor aswel

Example my old t3 20" remmag using 2225 was running almost as fast as 2 mates with standard 24" barrel t3's i think was about 15fps in it

I don't know about the fast/slow powder theory, but if I want to retrieve velocity in a shortened barrel I move from ADI single based type powders to the hot ones of around the same (previous) burn rate - Vihtovouri N series and Alliant and some Hodgdon.

How fast is the powder used for 22 rimfire ? Have read somewhere that max velocity is reached very quickly. Pistols would be the same ? So perhaps extrapolating that info would give you your answer Hermitage ?

[QUOTE=Danger Mouse;1194280]

Heavier projectile means slower acceleration. [QUOTE]

Not in practice i have found. See you stuff anything into the spare void in a case (be it more projectile or whatever) you get more pressure.
For example, try eld 140gn with 46gn of 2213. You will get say 2760fts. Use the same setup but swap in 147gn eldm's and you will get 2800fts from the additional pressure.

I have my chamber set up so that my lands still allow a regular 140 to have all the bearing surface of the neck touching bullet. The 147s end up down deeper into the case (just touching powder)

Here's my understanding (essay warning):

As you subject the powder to more pressure and more heat, it burns more thoroughly/cleanly/completely. Smokeless powder essentially creates its own positive feedback loop and this peaks well within the first few inches of barrel. If you cram more powder in (which takes up more case volume and more tightly packs the powder), use a hotter primer, jam the bullet into the rifling, or crimp the round heavily to hold it all in place a little longer, these things can all give the ignition a little bit of an initial boost, which can compound to have a big effect a few fractions of a millisecond later given the exponential nature of the combustion.

Maximum chamber pressure (pmax) is reached very quickly - GRT and QL will show this. Around pmax, the volume behind the bullet is growing as it moves down the barrel, most of the powder is already lit and the supply is dwindling, and so combustion can no longer sustain the growth. The positive loop is broken and turns negative. Pressure starts to tail off and the combustion rate of any remaining powder is going to drop off too... Important to note that even if the powder essentially goes out, the bullet is still getting accelerated since there's still tens of thousands of PSI behind it.

Not mentioned at the start was bullet weight. A heavier bullet has more inertia. Without any other changes to the load, the heavier bullet will contain everything in a tighter space for longer which reinforces that positive loop resulting in more pressure. You would need a slower powder to avoid going above pmax. Go the other way and drop in a lighter bullet (again, no other changes) and that feedback loop might peak at lower pressure - as the bullet moves down the barrel and volume opens up faster. You would need a faster powder to reach the same pmax. What proportion of the powder gets to burn in the SAME LENGTH OF BARREL here is dictated by the bullet weight more than the burn rate.

So pmax and 100% burn don't coincide and you may or may not get to 100% burn by time the bullet exits either. Most of what's going to burn, will do so very early on and the last bit may never finish regardless of barrel length (given the negative loop). GRT and QL both estimate the percentage that gets burned AND they also both show an "effective efficiency" percentage. I'm not sure how the latter is worked out, but it's likely along the lines of "what percentage of chemical energy in the powder has been turned into kinetic energy for the bullet". The two percentages are telling us different things and we fixate on them for the wrong reasons sometimes, depending on what we're after and our interpretations of the terminology...

Which powder gives the most speed? The bullet accelerates with area under the pressure curve over time. So the powder that produces the biggest most sustained high pressure curve gives the bullet the biggest kick and this award goes to the slower powder. This doesn't really change much by shortening the barrel until you get to really silly extremes, even with something obscene like a 50BMG. Sure, the % burn will drop at an increasing rate as you do shorten the barrel (negative curve) but the overall pressure curve will still have imparted more energy onto the bullet up to that point vs faster powder.

Which powder is most "efficient"? By QL/GRT definition, the fastest one. But we've just shown that most efficient != most speed. The faster powder's pressure curve will be sharper as the powder burns at an increased rate initially. But assuming we've dialled it down to reach the same pmax, the faster powder will hit that point sooner, having produced less gas, thus pressure tails off quicker. That's less area under the curve over time and therefore less speed.

E.g. if you have a 223 with a 75gr bullet and wanted best efficiency i.e. "best % burn and % energy transfer", then you might be tempted to use AR2219. You'd hit 62,000psi very quickly, probably get a 100% burn, and probably be >35% efficient. But if you wanted most efficiency" i.e. "most speed", then AR2219 is a bad choice, as it's unable to drive the bullet as hard for nearly as long within the same pmax constraint vs a slower burning <30% efficient powder like AR2206H could with a bigger muzzle flash.

So in summary:
1) Getting a 100% burn could be considered a bad thing if speed is the primary goal and we sometimes think that "100% burn means I don't need a longer barrel" which is massively oversimplified. It actually suggests a slower powder might have produced a more favourable curve and to obtain max speed, there will be a narrow range of powders (correlating with case capacity vs bore size) that will produce optimal pressure curves that will probably all blow a bit of unburned powder out of the muzzle.

2) Faster powders are more efficient with the same bullet vs slower powders and this has merits (less muzzle blast, flash, noise, easier on suppressors) but speed isn't one of them. Shortening the barrel makes these advantages more profound but still doesn't change which powder will deliver most speed.

3) Which powder you should use is dictated more by bullet weight than burn rate or barrel length. A similar amount of slow powder will burn behind a heavy bullet as fast powder will behind a light bullet, in the same barrel.

4) "Shorter barrels should use faster powders" either is or isn't a myth depending on your goal.

Thanks for listening to my TED talk... I should do some work now.

^^^ Very nice ted talk indeed. You are a man of patience and virtue. Unlike me - haha

That is good reading ^ thank you

^ testify

Wow @Pommy you have mostly restored my faith in this forum with that answer.
I even saved it to a .txt document so I can refer to it in the future

And Pommy you wrote your great reply 7 hours ago and there are no signs of the 'assumption' that a few members made that 'it will be ripped apart anyway" (so what is the use of posting...)

Originally Posted by 199p

Disagree i think its more of a cant be fucked because you give a long in depth answer and someone will just rip it apart anyway.

But to keep this post on friendly terms ....I appreciated your self-deprecating funny comment @Tentman

Originally Posted by Tentman

^^^ Very nice ted talk indeed. You are a man of patience and virtue. Unlike me - haha

Originally Posted by Hermitage

But a 'muzzle blast' according to Wikipedia is an explosive shockwave created at the muzzle of a firearm by gasses created by the burnt powder.

"In addition to the blast itself, some of the gases' energy is also released as light energy, known as a muzzle flash".

So all the powder must be burnt inside the muzzle. The muzzle blast/fireball is light from the gasses.... not burning powder.

https://en.wikipedia.org/wiki/Muzzle_blast

The hot gases may include CO and H2 which will ignite on contact with atmospheric oxygen, you might need a VERY long barrel for gases to exit below their ignition temperature.

But speaking of fast shotgun powders, I have some cans of Hi-Skor 700-X. Does anyone know data on such for plinking loads in a .308/.303?