General revolver questions.

H

hulley

New member
I've got a few questions for you revolver guys. I have a LCR and am planning a SP101 and GP100 purchase soon.

1. Does the cylinder give you more effective barrel length than the actual barrel length stated? When I measure a barrel from a semi-auto, the round fits inside the stated length. If you were to measure from the front of the round the length would be shorter.

2. Does porting lower the velocity? I've seen some porting jobs that run along the top of the barrel and almost run the overall length (especially on snubbies).

Thanks
Hulley
 
Autos and revolvers are just measured differently. When you talk barrel length in an Auto you just always include the 'chamber', in a revolver you don't. I have an idea the military started that because the piece including the chamber and barrel were all one unit. I think if you went to get that 'piece' off the shelf it was just called the barrel, not the barrel chamber piece. That's just a guess.
The old tests they did with ported vs unported barrels showed that the difference wasn't worth considering, other variables, like the brand of primer, type powder, even brand of case, effected velocity mattered more.
 
1. Revolver barrels are measured differently than those of most other types of firearms including semi-automatic handguns, rifles, and shotguns in that the chamber is not included in the barrel length. The correct way to measure a revolver barrel is from the rear face of the forcing cone to the muzzle.

2. Porting does not significantly reduce muzzle velocity so long as it's done correctly. Porting does, however, significantly increase perceived muzzle blast and flash. Also, a common complaint about ported guns is that the quickly deposit powder fouling on colored or tritium front sights and thus reducing the usefulenss fo that type of sight. Many people, myself included, discourage porting on a self-defense gun because, if the gun were fired from retention, it is quite likely that the porting will direct hot gasses and burning powder directly up into your face.
 
Thanks guys that answers my questions! I considered porting a SP101 2.25" which would be a carry piece but thats a very good point. Maybe I'll save that for the .44 thats on the list. :D
 
1. Does the cylinder give you more effective barrel length than the actual barrel length stated? When I measure a barrel from a semi-auto, the round fits inside the stated length. If you were to measure from the front of the round the length would be shorter.
Click to expand...

That turns out to be a stranger question than you'd think, but only in calibers that are normally semi-auto.

I'm converting a 357Mag wheelgun to 9mm using a Bowen cylinder blank and a new barrel in the proper .355 spec for 9mm.

Looking at performance data for 9mm rounds out of an S&W 9mm snubbie, the velocity tests say that it matches a 4" barrel Glock or the like despite only a 2" barrel.

The 357Mag cylinder has conventional revolver chambers. The tight constrictions at the end of the cylinder bores measure .357 more or less. This is called the throat. As is usual with revolver cylinders the inner edge of that final constriction is "pointy" inside.

But the S&W 9mm cylinder is a smoothbore "long throat" almost an inch long, of the proper width for a 9mm throat (either .355" or .356"). There's no "end constriction" in this sort of throat, the throat is actually that long.

Very obviously the bullet is accellerating down that long smoothbore throat, possibly faster on a per-inch basis than it would go from an equivalent length of rifled barrel as there's less blow-by.

This has interesting implications:

1) You could easily take such a cylinder and build a "pepperbox" gun out of it. It would be illegal as hell if the "barrels" were still smoothbore, but it would still be lethal at close range.

2) The bullet is therefore hitting the forcing cone (back of the barrel) at a higher rate of speed than with other more conventional revolver types. Not sure if that's an issue exactly...

Anyways. This explains why I'm re-building my gun as a 3.5" barrel - I'll then get bullet speed about on par with a 5" or more Glock, which is plenty for the 9mm.

I'm also cutting that "long throat" at .3555" the whole length.
 
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