Barrel Length

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MaduroBU
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Barrel Length

#1

Post by MaduroBU » Fri Jan 26, 2018 1:15 am

I have a crazy habit that I'd like to share and get thoughts on. When I consider a cartridge, I think of the barrel as part of the cartridge. For an extreme example, consider a .300 Winchester Magnum with a 30" barrel vs the same cartridge with a 6"barrel. One is unthinkablly short, the other is a touch longer than the norm but still within reason. Why? If we think of the brass case AND barrel as the same pressure vessel, the the expansion ratio for the powder gas generated by the combustion of the powder renders much of the powder wasted for a short barrel.

As a counter example, a 6" barrel .357 magnum is quite reasonable while a 30" barrel would be actually lose velocity vs, say, an 18" barrel due to losses from friction.

We are really constructing a pressure curve, with the max pressure set by the case strength and the length of time that our pressure differential is allowed to act upon the bullet set by barrel length. These are non-linear relationships, but higher values CAN lead to more muzzle energy. Mismatched, they can lead to a needlessly long gun or a gratuitous muzzle blast. Remember, powder gases exit the muzzle moving faster than the bullet and function almost identically to a rocket engine vs your shoulder or wrist.

Presuming that shorter length is desirable, as are high muzzle energy, low muzzle blast and low recoil, then certain features become more desirable. In trying to maximize the good and minimize the bad, higher pressure and a well matched barrel length becomes truly desirable. Further, when a short barrel is needed, a smaller caliber may be a better choice than a more powerful one.

By way of example, I love shooting my P226 X5 .357 Sig with a 5.7" threaded barrel. It is not a carry gun. Instead, I use a P232 stainless in .380 ACP. I find that a .380 is well matched to a 3.5" barrel and my recoil tolerance. Those are very different guns, but similar in that the barrel lengths are matched to cartridges for ballistic efficiency. In rifles, the new SBR craze has resulted in similar debates if more forgiving limits. Is a .308 with a 16" barrel an eardrum shattering masochist's weapon or a reasonable way to move the same .30 cal 150 grain bullet 500 fps faster than a .300 blackout of similar overall length?

What about a 24" vs a 28" magnum rifle barrel? Why do butt stocks get a free pass for chewing up inches of overall length?

Anyway, I'm interested to hear thoughts.

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Beiruty
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Re: Barrel Length

#2

Post by Beiruty » Fri Jan 26, 2018 7:04 am

For internal Ballistics and MV estimation for your firearm (barrel length, etc). load, etc..all what you need is to get a copy of the QuickLoad. There is free demo that limited to caliber and that you can play with. http://www.neconos.com/

I agree with you that some rifles are unnecessary long (unless you are F-class shooter with many years of handloading) or extremely short (AK pistol)

Shooting with factory ammo for unusual short length barrel or very long barrel is just unwise. This is where handloading comes in to remedy the problem.

24" vs 28" for mag rounds? If you handload and you are shooting from a bench or prone go with 28" with slow burning powder you extract some more MV.
Beiruty,
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AndyC
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Re: Barrel Length

#3

Post by AndyC » Fri Jan 26, 2018 10:59 am

MaduroBU wrote:...the expansion ratio for the powder gas generated by the combustion of the powder renders much of the powder wasted for a short barrel.
Depends on the burn-rate of the powder used versus the barrel length - as it's always been.
MaduroBU wrote:Is a .308 with a 16" barrel an eardrum shattering masochist's weapon or a reasonable way to move the same .30 cal 150 grain bullet 500 fps faster than a .300 blackout of similar overall length?
Everything's a trade-off ie. horses for courses - the .308 is a medium-length cartridge and needs a medium-length action. You want to use a 30-cal bullet/cartridge in a short AR-15 action, you gotta sacrifice some stuff.
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MaduroBU
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Re: Barrel Length

#4

Post by MaduroBU » Sat Jan 27, 2018 2:21 pm

Of course there are tradeoffs, but my point is that some are subjective. How desirable is efficiency? How awful is muzzle blast?

I was considering the K&M m17s, and the choice between a 16 or 20" bbl .308 vs a 17.5" bbl .300 Blackout forced me to think through these issues more carefully than I had in the past. For a group that carries guns around, the broad form of that question seemed interesting.

Thanks for the replies.

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AndyC
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Re: Barrel Length

#5

Post by AndyC » Sun Jan 28, 2018 1:22 pm

MaduroBU wrote:Of course there are tradeoffs, but my point is that some are subjective. How desirable is efficiency? How awful is muzzle blast?
As you said, it's subjective - that's one reason you tailor-make your ammo to suit your preferences.
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MaduroBU
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Re: Barrel Length

#6

Post by MaduroBU » Sun Jan 28, 2018 5:18 pm

AndyC wrote:As you said, it's subjective - that's one reason you tailor-make your ammo to suit your preferences.
And that's a great point. It amazes me how a caliber that may be marginal or otherwise suboptimal in the form that it commonly takes can be made into a great set of compromises with a few small tweaks. The corollary is the question: why are some calibers so badly misused by the people who should want to maximize them and should be the best at doing so?

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