Question about cylinder gap on revolver

[BCRider]

I've got a S&W model 28 that I got used. It's got a bit of cylinder end play that I want to shim out. The shimming out isn't the issue since that's pretty straight forward. However I gather this shims the cylinder to the rear and leaves me with a bigger than desireable cylinder to forcing cone gap. Is there a way to deal with that? My first thought is that I'd need to unscrew the barrel and cut the shoulder by one thread pitch and then screw it back in, check the gap or interference (far more likely obviously) and then dress back the end of the forcing cone to achieve the optimum gap and possibly redo the forcing cone to make up for the shortening of it. While I'm at it I'd ream or bore out the cone for the currently accepted angle for the known hot setup... whatever that is. I saw the angle in some other material but it escapes me at the moment.

Am I missing something or is this pretty much it in a nutshell?

 

[dfariswheel]

You'll also have ejector rod issues if you turn the barrel back one thread.
Remember, the S&W has the front latch that locks into the ejector rod.

A forcing cone of 18 degrees is about perfect for jacketed bullets, 11 degrees for lead.
Remember, the cone MUST be gaged, it can't be eyeballed, and mouth gaging is more important than degrees of angle.

 

[BCRider]

Hadn't thought about the ejector. Thanks.

If this goes ahead I would definetly make up a slug rod that is a light push fit into the barrel and then center the bore off that prior to any work including any extra cutting of the forcing cone. This would be if I didn't just splurge and get the Brownell's forcing cone reamer set.

 

[rcmodel]

this shims the cylinder to the rear and leaves me with a bigger than desireable cylinder to forcing cone gap.

Not necessarily.
End-shake is wear on the gas ring, which increases headspace and decreases barrel gap an equal amount.

If the cylinder gap was correct from the factory, end-shake doesn't make it bigger.

It actually closes it up when the cylinder is slid forward. This also increases the headspace beyond what it was before the end-shake increased.

What you need to do is measure the headspace with the cylinder all the way back, then measure the gap and see if it is still in acceptable limits.

The only way it can really get out of whack is if the frame stretched, or the ratchet star is worn excessively.

rc

 

[Jim K]

IMHO, most folks make too big a deal about end shake and cylinder gap, usually because they have read about them rather than actually run into trouble.

Yes, either can cause problems, but 99.9% of the time, they are not worth worrying about. Rarely, they may be gross, but that is pretty uncommon on a quality revolver even after a lot of use.

Jim

 

[BCRider]

OK, so I did some feeler guage measurements that I should have done in the first place. My apoligies for not including this info in the first place. Here's the story.

End play gaps between forcing cone face and cylinder:
Cylinder pushed forward- between .002 (non binding) to .003 (binds).

Cylinder pulled back- go-.008 no go .009

so depending on how you stack the go and no go measurements it's between .005 to .007 inch end play.

With the 28 the cylinder chambers are recessed for the rims so the cases sit down into the chambers fully. So it appears that only that center bearing area and the high points of the hand star takes the punishment rather than the rear faces of the cases unless the case is pushed back out of the cylinder to impact on the inside of the frame. From the look of the imprint around the firing pin hole this does appear to be the case but it's a faint mark so I'd guess that when it does happen it's a soft impact. So it would appear that the tips of the star points as well as the roughly 3/32 wide donut around the center pin is what is there to resist the backwards kick of the cylinder. And when I peer in the gap I can see the play there and the point where it touches the rear of the opening in the frame.

So, it would appear that I can shim it back by around .004 to reduce the end play so it doesn't wind up and slap back or I could see if I can buy a new ejector with a higher star and center bearing area that could be skimmed to fit. That should eliminate some or most of the rearward float and close the cylinder gap by about the .004 that it seems to need. I think I may look into that as an option as well.

All this is in stark contrast to my Model 19 which sits the case rims against the back face. There's a worn but still blue case mark around the firing pin hole in the frame and the same feeler guage test showed the following;

Cylinder pushed forward- .003 no bind .004 binding

Cylinder pulled back- go .005 no go .006

So that's a float of between .001 and .003 on that gun. Your basic "locked solid" feel to the user.

 

[rcmodel]

So it appears that only that center bearing area and the high points of the hand star takes the punishment rather than the rear faces of the cases

That is the case, regardless of whether the gun has recessed rims or not.

The only case that impacts the recoil shield during firing is the one under the firing pin.

At the moment of ignition, the case is pushed forward all the way into the chamber. Then at ignition, the primer backs out, then the case slams back against the recoil shield and re-seats the primer flush with the case head.

The other five rounds are just rattling around in the chambers, and have no bearing on supporting the cylinder.

But the fired case doesn't support the cylinder either.

The "headspace" always allows some slack for the case to move in the chamber, and the cylinder to move on the center pin.

The only "bearing surface" stopping rearward movement of the cylinder is the center of the ratchet star.
Not the case rim.

rc