Loss of pressure at cylinder gap?

J

johnwilliamson062

Moderator
Following a thread in the NFA section I wanted to know if anyone has tested this. My guess is the best way would be to shoot out of a revolver and Encore type gun with the same length barrel and check differences in velocity with identical loads.

I have just never really understood how revolvers can work if there is enough pressure leaking at the cylinder gap to make suppressors pointless.

I know you can get fine tuned competition guns with smaller gaps, that there will be some variance on calibers, etc, but I just wondered if anyone had data of this type for any caliber and gun as i would just like to get a "ball park" figure."
 
If i recall correctly the velocity drop isn't a whole lot. Im guessing 75 fps or so? There are revolvers like the nagant and webly that sealed against the barrel, but they didn't stick because they cost more to make and don't improve the proformance enough to matter.

I have no idea how much pressure is actually lost.
 
You don't lose enough for it to matter to the shooter or the target. The only thing affected by the cylinder flash is anything that happens to be too close to the cylinder gap when firing.
 
Skidder, great link. Thank you.

Looks like about 10%.
Seems like that should be about 10% of the sound then, right? NO not that simple... Anyone with more knowledge of physics want to take a stab at this?
 
the revolver might actually be faster. my normal 45 acp practice load is a 200 gr swc and out of a 5 inch 1911 it does about 900 fps. out of a sst blackhawk with a 4.625 barrel the same load is almost 1,000 fps. there are not any hard and fast rules about this. to know what you really have you have to buy a chronograph
 
Take a 7-shot Russian Nagant revolver (circa 1895-1950s? some are still in service), which are completely sealed (and can be fitted with silencers), shoot a regular Nagant cartridge thru it, then trim back the brass on another cartridge to re-establish the air gap, and shoot it.

Checked it out years ago....3% loss in velocity.
 
Other reports comparing the difference with the Nagant revolver suggest a greater difference, enough to make it worthwhile. Some Belgian made revolvers of the same sort did not have the gas sealing feature but the Russian and Soviet ones did. The caliber was exactly the same, since the Russian guns had a special cartridge but the were both small .30 caliber rounds. Either way, I've noted conflicting numbers regarding the velocity of the bullet but none were particularly powerful. Supposedly it remained fairly popular in Russia for a long time.

Another factor is that in measuring barrel lengths, the cylinder in a revolver is typically not included, so the real barrel length for a given nominal measurement is actually longer in a revolver.
 
There have been a few successful attempts at this over the years. Most recently Knight's Arament build a silenced GP-100.

Unless your objective is a suppressed revolver then any meaningful difference could be addressed during weapon development. You either increase the powder charge (.38 special +P, .357 magnum, etc.) or fire a heavier bullet slower, say .455 Webley, .45 Colt, .45 ACP, .44 Special, or .44 Russian.

Or you can go the opposite route and develop a very complicated revolver like the Nagant.

The .357 magnum without a cylinder gap would probably gain a few fps. Then again, .357 magnum can fire a 158 grain bullet at over 1500 fps if you're using the right load...cylinder gap and all.

That's plenty of performance without resulting to additional mechanical complexity.
 
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The velocity could likely be more effected by primer, powder and bullet than by the cylinder gap. As far a suppressing the noise, just fix a piece of Kevlar, say something like a thick washcloth size, over the area of the gap. If you're using something as bulky as a suppressor a little more bulk should not be a problem. I'd think a break open single shot pistol would allow the greatest reduction in dBs.
 
There was an article in Handloader magazine recently where they compared a Blackhawk, a S&W 625, a .45acp Contender and a 1911. All guns chambered in .45acp and had identical effective barrel lengths, that is all four had the same distance for the bullet travel to the muzzle.
The Blackhawk had about a .003" cylinder gap, the 625 had about a .008" gap.
The 1911, the Contender and the Blackhawk all had identical velocities. The 625 was about 10% slower.
 
YOU should wrap your mind around this. PEAK pressure is achieved before the the bullet clears the case.
And now this: the revolver reaches higher peak pressures in the chamber than the automatic pistol chamber reaches. NO FOOLIN'!!
And so it goes...
 
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