Semi-Auto and Revolver Barrel Lengths

[usnavymasterchief]

Perhaps someone can answer this question about the differences in measuring barrel lengths on revos and semi-autos.
My Kahr K40 advertises a barrel length of 3.5" while the actual rifled length of the barrel is only about 2.25", if you measure the chamber and the rifled portion it is in fact about 3.5"
My Taurus 651 revolver advertises a barrel length of 2" and the rifled portion is just that, 2". If revo makers used the same standard of measuring their barrels that semi-auto makers use and measured the length of the cylinder and the rifled portion of the barrel, my Taurus barrel would be about 3.5".
How come that is????

 

[BigG]

I think it's because the chamber and bbl are one piece in an auto whereas a revo has a separate chamber, i,e., the cylinder. In a rifle, chamber is included in the bbl length. HTH

 

[C.R.Sam]

BigG right.

Sam

 

[ceestand]

Though, this brings to mind the thought that a "4-inch" revolver and a "4-inch" semi-auto could potentially have drastic differences in performance based on barrel length alone. Yet, due to their designations, may be considered equals, depending on purpose.

 

[Nightcrawler]

So here's the question. You have two .45ACP handguns, one a revolver with a 4" barrel, the other a semiauto with a 4" barrel.

So the revolver has higher muzzle velocity, because it has 4" of actual, bullet-goes-down-this-part-of-the-tube barrel, whereas in the semiauto you have to subtract, from the 4", the length of the chamber.

Correct?

 

[4v50 Gary]

Not necessarily. Gas leak from the barrel/cylinder gap. TANSTAAFL.

 

[Shawn Dodson]

A semi-auto barrel is actually a barrel "assembly", comprised of two parts: 1) the chamber, and 2) the barrel.

Washington state used to require a minimum barrel length for handgun hunting. A game warden cited a hunter who was hunting with a revolver whose barrel length didn't meet the minimum requirement. The hunter went to court and argued that, by using the FBI's method of measuring barrel length (inserting a rod into the muzzle until it stopped), his revolver met the minimum requirement. The hunter won the case and Washington eliminated the minimum barrel length requirement.

 

[ceestand]

inserting a rod into the muzzle until it stopped

With a round chambered or no?

 

[Standing Wolf]

With a round chambered or no?

No.

 

[Preacherman]

This is actually a thorny legal issue in many places (e.g. Canada, where minimum-length requirements for handgun barrels are an issue). With a semi-auto, one drops a dowel down the barrel until it meets the breechface, marks it at the crown, and then measures the length from the mark to the end that contacted the breechface to get the barrel length. However, with a revolver, typically one measures from the crown to the forcing cone to get barrel length, leaving out the cylinder. Thus, a 5" barrelled semi-auto is NOT equivalent to a 4" barreled revolver, as the former includes the chamber, but the latter does not.

It's a legal anomaly which I hope will be cleared up someday. In the meantime, watch out for the bureaucrats doing the measuring...

 

[Archie]

The measurements are arbitrary....

I suspect they stem from very long ago and hold on just because "that's the way we do it".

When playing with internal ballistics, the length of the barrel is measured from the base of the bullet to the end of the muzzle. (That is the distance the expanding gasses push on the bullet.) So, comparing a five inch barreled revolver to a five inch barreled auto is misleading. The revolver has more useful barrel.

 

[Majic]

(That is the distance the expanding gasses push on the bullet.) So, comparing a five inch barreled revolver to a five inch barreled auto is misleading. The revolver has more useful barrel.

True, but the revolver doesn't use the advantage efficiently so the playing field evens between the 2 handguns.

 

[Gabe]

On some aircraft revolver cannons the shell is pushed forward when fired so the case neck bridges the gap.

 

[Archie]

Going to have to do some testing....

quote:
--------------------------------------------------------------------------------
(That is the distance the expanding gasses push on the bullet.) So, comparing a five inch barreled revolver to a five inch barreled auto is misleading. The revolver has more useful barrel.
--------------------------------------------------------------------------------

True, but the revolver doesn't use the advantage efficiently so the playing field evens between the 2 handguns.

But the autopistol uses up some of the cartridge energy in operating the pistol. Or so goes another old theory in this matter.

My experience and research indicates neither of these is perfectly so. I've read several tests wherein revolvers with "shorter" barrels gave higher velocities than autos with "longer" barrels. And I've seen evidence that an auto outran a revolver in a similar test.

The results show that individual differences in guns make more difference that the "average" difference between revolvers and autos.

I'm going to have to scrounge up several revolvers and autopistols in similar or same calibers and do some chronograph work. I have revolvers and autos in 22lr and 45ACP. I have a 9x19 pistol and a couple 38 Special revolvers of various lengths. Sounds like a project.