Cylinder gap loss

[Brick]

Did you ever wonder how much is actually lost because of the cylinder gap in a revolver. Just for grins and giggles I chronoed a single load
of 9mm to compare between a 5" barreled S&W 986 9mm Luger and a 5" barreled CZ 75b 9mm.

The bottom line? The revolver averaged less than 40 fps slower than the semi. The load was a Penn Bullets 120 gr. cast lead Truncated Cone ahead of 4.7 grs. of Hodgdon CFE-Pistol. Take note that even with the loss that load still exceeds the old IDPA 125,000 power factor.

Please be sure to look at the pdf.

[frankski]

How do you feel about not including the cylinder as part of the barrel length in the comparison?

In any case, I see your point. Not much difference.

[DucatiRon]

Actually one of the reason I like Dan Wesson Revolvers. While the cyl gap loss isnt much being able to adjust the gap is a plus in my book. Consistancy leads to accuracy.

[Gunsnwater]

Still the stuff flying out the gap will put a real hurting on you.

Hickok has 2 videos on it.

[98Redline]

http://www.ballisticsbytheinch.com/gaptests.html

[Bang]

Damned interesting. First it has been pointed out (for me) that part of the revolver...the chamber...takes the place of a semi-auto barrel chamber, effectively lengthening the gas-driving bore behind the bullet. That tends to make up some of the gap loss.

It all serves to illustrate the need to load for the gun. Yet, loading for the gun is dangerous. The load could easily be used in a different gun, creating a kaboom potential.

The charts show the importance of a chronograph. If a bullet opens at 900fps but not at 825, that's a need to know. And if barely above the needed velocity, deviation means some will open and some will not.

It all adds up to use the handgun to get to the rifle.

[Brick]

I can't even guess why the revolver cylinder is left out of the "barrel length" dimension. Except that they're separate parts and some holster maker long ago started the trend.

In this case I can reload to my desires for the revolver and know I get the performance I need from the semi-auto. But there are still questions I wish I had answers for. Referring to some of those great Mythbusters slow motion shots of revolvers firing. The first thing we see is a puff of something before the bullet and burning gas appear. I think that is likely air being displaced from the barrel by the bullet. But I'm still not sure if the bullet is out of the barrel before gas starts to leak out of the gap. Also how much does the passage of the bullet seal the gap as the bullet is driven forward.

[98Redline]

But I'm still not sure if the bullet is out of the barrel before gas starts to leak out of the gap. Also how much does the passage of the bullet seal the gap as the bullet is driven forward.

As soon as the bullet jumps the B/C gap you will start to get gas leaking out. If you look at some of the really high speed stuff, you can see the blast before the bullet leaves the muzzle.

As far as how well the bore is sealed by the bullet, in most cases it is sealed darn near 100%. The notable exception is when shooting a cast lead bullet that is undersize for the bore or is too hard to obturate properly, in this case you will get some hot gas jets getting by the bullet (one of the many causes of leading with cast bullets).

...The load could easily be used in a different gun, creating a kaboom potential.

Unless you are teetering around at the very tippy top end loading for a particular bullet/powder combination, most loads should be perfectly safe to fire out of any revolver. There are "Ruger / Contender only" loads for calibers like 44mag that may beat up a S&W a bit but should be quite a ways from a proof load and certainly a "kaboom" load. All of the revolvers I have heard of or seen destroyed by a load were all massively overcharged or double charged and would have likely blown up anything. That is not to say that you want to feed your S&W Model 29 (no dash) a steady diet of Ruger only loads, just that a couple cylinders full is not apt to blow the gun up.

[Brick]

Yeah 98, but damage doesn't have to be a total KB to disable a gun. Look at this photo. This occurred to me several months ago. The gun is a Model 10-8, the load in use was a 125 gr plated truncated cone bullet over *7.2grs* of A#5 a maximum load. I don't believe I was double charged, but it is possible to have been overcharged by an unknown amount into +P or +P+ range. Very disconcerting since the Model 10 and the old Model 13 (.357 Magnum) were the same gun (the M13 just had a lengthened chamber, but not a lengthened cylinder).

[MARINE DIVISION TWO]

Still the stuff flying out the gap will put a real hurting on you.

Hickok has 2 videos on it.

Spitting lead outside the gap is a bitch digging out of the fingers and hands !