end shake and shimming yoke

[vzeoah]

A question. (Maybe should be put in the gunsmithing forum)? I watched a video by Larry Potterfield, from Midway. He shows how to get rid of excessive end shake in a S&W revolver. Correct me if wrong, but doesn't this do so by shimming the cylinder at the end of the yoke, thereby putting the cylinder always further back in the frame? In other words, keeping the cylinder/barrel gap opened up at maximum all the time? If I am correct, and have excessive cylinder/barrel clearance, isn't this is pointless?
P.S. I will post on a few other forums, too, for those that read others as well.

 

[500 Magnum Nut]

doesn't this do so by shimming the cylinder at the end of the yoke, thereby putting the cylinder always further back in the frame? isn't this is pointless?

Yes your correct on the gap getting bigger, but the gun needs to run with min end shake. Too much causes weird problems, such as it could mess up the timing and cause misfires etc.
So if your gun has a large gap, the barrel needs to be removed and cut back, then reset to a .003 gap. Your end shake needs to be no more than .002. There are different ways to adjust that, from peening the yoke, stretching with a special tool or adding shims.

 

[bountyhunter]

End shake is a lot more harmful than a slightly wide barrel gap. B/C gap can be as wide as .010" - .012" and not affect muzzle velocity much. End shake needs to be addressed if it is over .002".

 

[S&W revolverman]

Acceptable b/c gap, by the factory. minimum.004 - maximum.010.


Hope this helps
chris

 

[bountyhunter]

It's true that SW has traditionally quoted .004 - .010" as the range of BC gap. However, I know of new guns with .012' gaps returned to SW by annoyed buyers who had them shipped back unchanged as being "OK". It doesn't affect performance much.

I have seen actual test data on some revos where the BC gap was increased from about .004 to about .012" an the effect on muzzle velocity is small like maybe 15% or so min to max. The BC gap acts as a gas vent for the gas load that is driving the bullet out the barrel, and losing some pressure there does lose a bit of propulsion force but not a huge amount.