Insufficient B/C gap on M&P Target

[donaldw870]

I have a 1905 4th change M&P Target from ca. 1928 with a barrel/cylinder gap problem. On one side, it's .001 at best (yes, I used feeler gauges) and the other is maybe .002 or .003, depending on which chamber is in firing position. After one cylinder full, the crud has built up to the point that it severely affects the trigger pull. I want to be able to shoot this gun fairly regularly because it's very accurate, and it has the very smoothest action of any of my M&P revolvers (when not fouled).

I know I could take a file to the barrel, but I worry that the problem is actually a misaligned cylinder, given that the b/c gap changes as the cylinder rotates.

Does anyone have any advice for what I should do about the problem? If it's a misaligned cylinder, it's beyond my ability to repair. Might S&W be willing to do the repair?

Thanks for any input.

Donald

 

[Alk8944]

I have a 1905 4th change M&P Target from ca. 1928 with a barrel/cylinder gap problem. On one side, it's .001 at best (yes, I used feeler gauges) and the other is maybe .002 or .003, depending on which chamber is in firing position. After one cylinder full, the crud has built up to the point that it severely affects the trigger pull. I want to be able to shoot this gun fairly regularly because it's very accurate, and it has the very smoothest action of any of my M&P revolvers (when not fouled).

I know I could take a file to the barrel, but I worry that the problem is actually a misaligned cylinder, given that the b/c gap changes as the cylinder rotates.

Does anyone have any advice for what I should do about the problem? If it's a misaligned cylinder, it's beyond my ability to repair. Might S&W be willing to do the repair?

Thanks for any input.

Donald

First, S&W won't touch it since they have no parts for guns that age.

Second, a cylinder that does not have a completely flat face is not unusual. The blanks aren't lathe turned to square the faces. My much later 631 is out of square by about .005!

Third, have you checked the cylinder for end-shake? Try moving it lengthwise in the gun with the cylinder closed. If there is more than just barely enough to tell it is moving you need to address this problem, which will push the cylinder toward the breech and away from the barrel. The easiest way is to use end shake bearings available from Brownell's. I am willing to bet you will find the gun has excessive end-shake which is much more likely than a gun this age having only .001-002 flash gap.

 

[bountyhunter]

+1 on the end shake, that's almost surely where the B/C gap went to.

 

[WR Moore]

Given the age of the revolver, and possible collector value as is, do you really want to mess with it? If so, keep reading.

FIRST: Get access to a yoke alignment spud, check that the yoke lines up properly with the center pin hole. If the cylinder sits in the frame at an angle, you're going to get an uneven b/c gap under any circumstances.

Besides endshake, check the yoke for proper fit to the frame. Power Custom makes shims to put the yoke shoulder against the frame like it's supposed to be.

If your cylinder face is uneven, DO NOT USE A FILE! You need the services of a machinist to make sure the rear of the cylinder is square to the axis of rotation. If so, the face can be either turned or surface ground (best) to an even surface. Very careful stoning can correct small problems, but it's tedious work.

 

[donaldw870]

Thanks for the replies. I checked the revolver over pretty well before I bought it and didn't notice any endshake, but I'll double check. That sounds like the best explanation, and the easiest problem to fix.

As for the yoke alignment, I'll look into that too. I agree that I need to think about whether I want to mess with it. It does have collector's value, being pretty high condition.

Donald

 

[donaldw870]

Endshake is the culprit

Well, I checked the revolver in question for endshake today, and compared it to my other revolvers, and I'm pretty sure it's an endshake issue. Looking closely, I can clearly see that the B/C gap closes up to nothing when the hand engages the star. I didn't realize just how little front-to-back play constitues a pretty serious endshake issue, but now I know.

Thanks for helping me figure this out. I think this is a repair that even I'll be able to do. I'm sure that I'll be back in this room to ask questions when I get around to it.

Donald

 

[dant]

not being a fan of 'shims' in the yoke/crane, especially for any duty or defense gun, I would just do it the old fashioned way and stretch the upper crane leg, the way they taught us years ago...still works for us

 

[bountyhunter]

Stretching is a good fix, but it requires the precision fit rod to go inside the tube so it won't be damaged while peening. It also requires a cutter that can square the newly peened end off dead square. Most home gunsmiths don't have these.

 

[HEADKNOCKER]

Here's a small video that show rather quickly how to install the Power Customs end shake bushings..
Your 1905 4th change will be Right hand threads on the ejector rod..
YouTube - Gunsmith - Fix excessive cylinder endshake in S&W revolver
Enjoy!!

 

[donaldw870]

Thanks much for the continued input. I'll consider the possibilities and will be back here this winter (when I anticipate I'll finally get around to it!) for more help.

Thanks,
Donald