energy loss due to barrel / cylinder gap

[max popenker]

Hello

does anybody know reliable numbers for bullet energy loss in revolvers due to propellant gases escaping through the cylinder/barrel gap?
I'm interested in both modern revolvers and revolvers made a century ago - basically i try to understand if the whole 'gas seal' business with Nagant M1895 revolvers was worth a penny or not.

Thanks

 

[MikePGS]

Hey Max. Theres a couple of members who seem to have formulas that factor in cylinder gap. Not sure exactly if this will solve your problem, but the issue is addressed a bit in this thread http://thehighroad.org/showthread.php?t=361714
Btw love the website.

 

[General Geoff]

Realistically, you're looking at 100-200fps loss, depending on the caliber, projectile mass, powder type, and velocity. It also depends on the barrel-cylinder gap size. A tighter gap will result in less loss.

 

[Old Fuff]

Unless the gap is excessive (over .010") I think the loss is less then some think. Each revolver is different in things such as chamber throats and bore diameters, and these have an effect too. Sometime back, someone took a Dan Wesson revolver that was designed so the barrel gap was user-adjustable. Using the same ammunition he adjusted the barrel going from a very tight gap (.0015") to (.012"). There wasn't much change in velocity until the gap got into the (.006") range, but then it became noticeable.

Because of the use of unjacketed, soft lead bullets and black powder during the 19th and early 20th centuries, barrel/cylinder gaps often ran between (.008") and larger. Today's revolvers are usually made much tighter.

 

[Deer Hunter]

Realistically, you're looking at 100-200fps loss, depending on the caliber, projectile mass, powder type, and velocity. It also depends on the barrel-cylinder gap size. A tighter gap will result in less loss.

That number seems to have been pulled out of thin air. I highly doubt it's that much.

A good test would be to look at the difference in velocity between a Smith and Wesson 610 and a 10mm Auto with the same barrel length.

 

[Old Fuff]

A good test would be to look at the difference in velocity between a Smith and Wesson 610 and a 10mm Auto with the same barrel length.

Not really, because the difference could reflect differences between the two handguns besides the revolver's barrel/cylinder gap. Also the pistol's barrel length includes the chamber, while the revolver's does not.

 

[General Geoff]

4" Smith & Wesson 610, vs a 5" 1911. The 10mm Auto case is almost exactly 1 inch long (25mm). So if the 1911's barrel length includes the chamber, the rifled portion of the barrel would be the same length down to 0.4mm.


Anyone who has both of these guns and a chrono: You have a job to do!

 

[7.62X25mm]

Gas seal in the Nagant is an unnecessary complication. It does improve velocity, but you can do that with a heavier load.

Sometime shoot your revolver in the dark and get a look at the blast around the sides of the cylinder. There's the reason why in a cap & ball we seal the face of the cylinder to keep from igniting the other charges.

 

[unspellable]

I ran actual measurements in Dan Wessons with 22 LR and 44 Mag, the latter with a not overly hot factory load. Also a 22 LR pistol as control. The difference did not come to much. Cylinder gap varied from 0.002 to 0.012. Rub is, I just moved and can't lay hands on my data. I can say that at 0.012 both revolvers began to spit badly.

 

[bluetopper]

Shooting same ammo, 45acp 200gr lead SWC.

6.5'' Taurus 455 revolver.........1018fps

5'' 1911.......968fps