As I understand it, when the barrel length of a revolver is given, it's the distance from the front of the cylinder to the end of the muzzle.

But what about a semi-auto pistol? I think you measure from the base of the cartridge in the chamber to the end of the muzzle.

So to make a comparison, when comparing barrel length of a revolver to an auto pistol, a better comparison would be from the back of the revolver cylinder and the base of the bullet to the muzzle.

In other words, when my 2" 31-1 is shooting 32acp it would be approximately the same ballistics as a 3" semi-auto because of adding the (approx.) 1" cylinder to the two inch revolver barrel.

Is this making sense, or am I off base somewhere?

Dave

You are describing how revolver vs. semi-auto barrels are measured. Someone has probably done the comparison you mention; I think the difference between a 2" revolver and the 3" auto would be the barrel-cylinder gap, so everything else being equal (ha!) the auto would have the ballistic edge. Lots of variables here.

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Alan
SWCA LM 2023, SWHF 220

I don't know about comparison of ballistics, which I think is what you're wondering. From what I've read, I would suspect that the ratio would be the opposite, that a longer revolver barrel length would be similar to a shorter pistol barrel. Hope that made sense (I'm not so sure!)
The semi barrel measurement is the length of the barrel to the end of the chamber. Not a huge difference from what you wrote, but some pistols have less support for the base of the cartridge than others, so there will be a difference in the small fraction of the brass that's exposed.

The web site "Ballistics By The Inch" has a page on Cylinder Gap. The semi-auto pistol uses some of it's energy to ejected the spend casing and rack the slide. How does that effect the ballistics?

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Have Gun Will Carry

On the other hand........

in both cases you are measuring the length of the barrel ..... you don't want to add the cylinder or try to subtract the chamber..... these "rules" are the standardized way (BATF) has established to measure and record a firearm's barrel length.

The ballistic effect is a whole different issue with revolvers loosing gas because of the cylinder gap and automatics using some pressure to work the action.

Will,

In a locked breach semi, link, cam or linkless, the barrel and slide will travel together some distance before unlocking. This in theory will not lose much combustion energy for velocity, if that is your question as most all of the gases are expending on pushing the bullet. A fixed barrel straight blowback should also lose limited pressure on the bullet, as long as you are not do silly things with reloads.

I am sure someone will come along with a vector analysis and tell me I am full of beans, but the practical differences would probably be eaten up by the usual overall differences between even the same make of gun.

Craig

Yes, you're basically right. See above in yellow.

The 5 inch barrel on a revolver does not count the cylinder. The 5 inch barrel on an auto counts the chamber. So on a 5" revolver, the length of the rifling is right at 5 inches. On an auto, the length of the rifling is the barrel length minus the cartridge overall length. Since the auto does not have a gap, the velocity for a 5 inch auto will be very close to the velocity of a 5 inch revolver. Maybe a little more, maybe a little less. Probably no more difference than the variation between identical guns. Two 5 inch revolvers will probably never yield the exact same velocity due to small variations in the barrels and the fact that one may be smoother, one may have been fired more, one may have a slightly different cylinder gap. If you want to compare apples to apples, you would compare just the length of the rifling. If that is close to equal (say a 5 inch 45ACP auto and a 4 inch 45ACP revolver) the advantage should be with the auto. Other factors such as depth of rifling, smoothness of the barrel or rate of twist may make one or the other come out ahead. Another difference in auto vs revolver, a 4 inch barrel 45ACP double action revolver (325 Thunder Ranch) has an overall length of 9 1/2 inches. A 5 inch Colt 45ACP auto has an overall length of 8 1/2 inches. Single Action revolvers are even worse with a 4.62 inch Vaquero having an overall length of 10.25 inches. So even though the auto is giving up a little rifling length to a similar barrel length revolver, it is still a little more compact. Always remember, autos are a passing fad.