Barrel Lengths and Round Effectiveness

[DonNikmare]

Most discussions on the effectiveness of cartridges (in handguns) seem to focus on calibers, grns, etc.

In reviewing some testing tables and results it seemed the length of the barrel made a very noticible difference to how the cartridge performed - expanded didn't expand, etc.

So what about them barrel lengths? Is there a length that provides the best potential for effective cartridge performance.

I never liked math and the whole equation like thinking...caliber grn load barrel length rate of rifling per certain distance = penetration, expansion, energy, etc. is just giving me a headache.

Just looking for some clarity if there can be clarity with this set of topics.

Nik

 

[tbeb]

I say 4" barrel for a revolver.

 

[Preacherman]

Don, it's all a question of how fast the powder in that particular cartridge burns. With so many powders available, one can choose a propellant that will burn up completely in 2" to 3" of barrel, or one can choose a slow-burning propellant that will still be burning when the bullet exits a 12-inch Buntline Special barrel!

In defensive loads (for example, Winchester Ranger SXT), manufacturers often use faster powders, as they know these will be used in carry guns with shorter barrels. In hunting rounds (e.g., from the same manufacturer, Winchester Partition Gold) the rounds will be loaded with slower-burning powder, as hunting guns typically have barrels of 6" or longer.

Firing a round with slow-burning powder through a short barrel produces lower velocities, much bigger muzzle flash and blast, and possibly accuracy difficulties too. Firing a fast-burning powder through a long barrel is less than optimally efficient, because after the powder is burned up, friction on the bullet from the walls of the barrel could actually cause it to slow down slightly before it exits the muzzle.

 

[russlate]

So does anyone have guestimates of the velocity increase:

1) from the typical 2" 25 acp barrel to a 4" barrel? Some 25's have aftermarket barrels that length. I have one.

2) from the typical 3 & 3/4" 32 acp to a 6" barrel? The Holy Grail of my era's shooters was the K-32, which I never attained. But I did grab a Beretta Model 100 with 6" barrel, target sights, etc.

3) for that matter, what length is the Beretta Tomcat's barrel and how much does it lose at that length from the typical 3 & 3/4" barrel.

Would it affect performance with modern ammo?

 

[Jim March]

The first question is "how fast does this round need to move to expand?"

Then you ask "what barrel length do I need to get there at low enough pressure that the gun doesn't blow up?"

You can always cram more powder in the case until the round moves quick enough - unless the gun chernobyls on you first. VERY careful powder selection can help keep peak pressure down - you can run more pressure over a longer time period and get more net energy than a higher-peak-pressure load, yet not blow the gun - but pressure control at this level basically requires factory ammo designed with high-end pressure testing gear NOT available to the handloader.

Example: Buffalo Bore is now taking orders for 158grain lead gaschecked semi-wadcutter hollowpoints rated for 1,000fps from a 2" barrel. And they claim it's no worse on the gun than any other 38+P load. There is NO way a handloader could safely work up a load like that...utterly impossible.

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Every caliber has a "sweet spot" barrel length that factory rounds are generally designed around. 357Mag combat loads are designed around a 4" tube, hunting in the same caliber are tuned for 6". 45ACP is traditionally 5" but there's lighter loads tuned for 3" - 4" range. 44Mag, typically 6". Picking "known good" ammo is easier if your barrel length isn't "odd for the caliber" but you can USUALLY adapt. A rule of thumb is "shorter barrel, go lighter, longer barrel go with a TOUGH projectile (Hornady XTP and Speer Gold Dot are two favorites) but some calibers are exceptions, such as the 158+P leads that work in 2" 38s.

There is NO "one right answer" across all calibers and needs. And the barrel length question can't be divorced from issues relating to the projectile and powder charge - they're all elements of the same issue.

 

[Jim March]

The "rule of thumb" is 50fps for every inch of handgun barrel, within reason.

"Reason" means that if your barrel is running WAY past what that caliber normally runs, then the powder charge is going to run out of steam before the bullet clears the muzzle.

Most 32ACPs run 3" - 4" barrels, and there's not a lot of case capacity. You should see a velocity boost with a 5" barrel but at some point past that you're into diminishing returns - probably at 6". At least with factory ammo - a careful handloader could adapt a charge to a longer tube (slower powder, etc).

Rounds with bigger case capacities like the 38Spl, 357 and such can pick up speed all the way down a carbine barrel length, though the last 6" or so won't be gaining 50fps per inch.

 

[PCRCCW]

Jim and others covered it very well....there is not a real "this is the way it is" answer. Powders, barrel designs, bullets etc all have an effect on how it turns out. Shoot well.