Model 65 with .002 B/C gap

[zach_c]

I just purchased this gun. Timing, lockup, trigger, bore, everything looks really good. Using an automotive feeler gauge, I measure the B/C gap on each turn of the cylinder and the gap was .002 every time. I again measured with the cylinder pulled back towards the firing pin side and the gap was still .002. If I understand correctly that means 0 endshake. There is no play in the cylinder front to back. I tried the .003 on all as well and never could get it in. I have seen several references that indicate .003 or .004 to .007 B/C gap is ideal. Also the headspace is .016. I realize I may have to clean the cylinder face after so many rounds to keep it functioning.

1) Given the gap, is the gun safe to shoot?
2) Will the gap ever potentially decrease with shooting or will it likely increase?
3) Is there an easy way to increase the gap to within spec or should I just leave it?

 

[Hapworth]

Barrel-cylinder gap: measured with the cylinder held back far as it will go.

Endshake: measured with barrel held back far as it will go, then held forward far as it will go; subtract and the difference is amount of endshake.

Properly measured, b-c gap of .002 is very small, but not unsafe -- just increases the chances of binding as unburnt powder and spent gas detritus builds up.

The b-c gap will not decrease; with much shooting, it will begin to increase and endshake sets in.

If, as you re-measure checking for endshake, there is truly zero endshake, this can be a problem as there should be .001" endshake or there's risk for binding under thermal expansion. A qualified revolversmith can, with a few special tools, quickly and inexpensively set the endshake to the proper spec, adding .001"; this will also add .001" to your b-c gap. This is done by shaving .001" off the yoke barrel face (not to be confused with the barrel face) and truing it.

Does your Model 65 have recessed charge holes? That would explain your headspace measurement, which is otherwise much too small for a non-recessed cylinder; non-recessed cylinders should have headspace of go-no go between .060" and .068", and recessed ones (if I recall) between .012" and .018". Headspace needs to be measured at the upper right rear of the cylinder, between the cylinder and the blast shield.

Perhaps, if your cylinder isn't recessed, you measured headspace with shells in the charge holes? That's often confused for headspace, but is actually shell clearance, a different measurement.

All told, though, it sounds like your 65 is good to go provided you keep it clean; if endshake is truly zero, that's the only thing I'd seek to remedy.

 

[wolverine]

Moring zach_c;

That is pretty darn tight, especially if you intend to shoot lead bullets.

Before moving on or trying to correct, first make darn sure that you don't any junk or crud caught between the ejector star & the rear of cylinder as that can both remove end shake & tighten the cyl/to barrel extension gap.

 

[zach_c]

OK, I cleaned the cylinder face and forcing cone as well as the ejector star, however none of them appeared dirty. I then re-measured, as describe by Hapworth, and it still measures at .002 with cylinder back as well as cylinder forward, on all chambers. My previous shell clearance measurement of .016 was with snap caps in place and is a non-recessed cylinder. Headspace is between .060 - .067 (my gauge doesn't allow me to be more precise). This gun has certainly had some use as there are rings on the cylinder face.

"shaving .001" off the yoke barrel face (not to be confused with the barrel face) and truing it"

So, where is the "yoke barrel face"? Is it still safe to shoot with 0 endshake?

 

[snowman]

So, where is the "yoke barrel face"? Is it still safe to shoot with 0 endshake?

Sir,

The yoke barrel is the hollow cylindrical component which fits inside the center of the cylinder, on which the cylinder turns. The face is the rear end of the yoke barrel, which contacts the inner surface of the center of the cylinder(confused yet?). Removing .001 of material from the face will allow the cylinder to move that much fore and aft, creating the .001 of endshake which is recommended.

The gun will be safe to shoot with no endshake, but, as it heats up, the yoke barrel will press more firmly against the cylinder, and the cylinder against the recoil shield(flat part of the frame immediately behind the cylinder), making the cylinder harder to turn or open. This is the "thermal expansion" of which the gentleman wrote earlier.

Regards,
Andy

 

[Hapworth]

OK, I cleaned the cylinder face and forcing cone as well as the ejector star, however none of them appeared dirty. I then re-measured, as describe by Hapworth, and it still measures at .002 with cylinder back as well as cylinder forward, on all chambers. My previous shell clearance measurement of .016 was with snap caps in place and is a non-recessed cylinder. Headspace is between .060 - .067 (my gauge doesn't allow me to be more precise). This gun has certainly had some use as there are rings on the cylinder face.

"shaving .001" off the yoke barrel face (not to be confused with the barrel face) and truing it"

So, where is the "yoke barrel face"? Is it still safe to shoot with 0 endshake?

As stated, yes, it's safe to shoot with zero endshake -- you're just more likely to experience binding from thermal expansion coupled with build-up in the small b-c gap.

Your headspace is in spec based on your description, and on a stainless cylinder one cylinder-full of fired rounds will leave carbon rings on the face, so your revolver may be quite fresh despite the scoring; certainly from the specs you report it sounds so, or has been mechanically refreshed.

The yoke is the arm that swings in and out of battery when you open and close the cylinder; the yoke barrel is the metal, tubular axis that the cylinder rotates on; you can see it entering the center hole of the cylinder's face. The yoke barrel face is the far end of the yoke barrel inside the cylinder.

Shortening it properly takes the correct tools and knowledge. If you have it done, use a qualified revolversmith, or do your homework first and buy the right tools if you intend to do it yourself.

But first, take it to the range -- all of this might turn out to be a non-issue if your 65 shoots true.

 

[jaymoore]

I'd shoot it first to see what happens. Run a bunch of rounds in short order. If it starts to bind, then it'll need a bit if loosening up.

Note that if you remove metal from the yoke face, then it's likely the cylinder will contact the barrel! So the barrel will need a bit of attention as well.

As a used revolver, I suspect you may find the cylinder may have had some Power Custom endshake bearing shims installed. They are hard to detect, as they slip down the central bore of the cylinder and rest against the internal face. Work great, but it's easy to put too many in. (Too much of a good thing and all that...) If you've disassembled cylinders before, it's no biggie, otherwise let your 'smith do it. A curved dental probe works well to remove them if they're installed.

As for the barrel face contacting the cylinder, you can move it forward yourself with a small file, patience, narrow shim stock and some marking compound. (Magic marker actually works fine.) A steady hand, a light touch and multiple trial fits is the secret to doing this job. Or you can use the cubic money method. (i.e., fancier tools or hiring it out.) Quite frankly, the "file method" done properly can do better work that some of the bore riding facing tools.

But, again, give the revolver a good wringing out at the range before doing anything else.

 

[friendlyfire]

This is something I would strongly consider...
"As a used revolver, I suspect you may find the cylinder may have had some Power Custom endshake bearing shims installed. They are hard to detect, as they slip down the central bore of the cylinder and rest against the internal face. Work great, but it's easy to put too many in. (Too much of a good thing and all that...) If you've disassembled cylinders before, it's no biggie, otherwise let your 'smith do it. A curved dental probe works well to remove them if they're installed."

 

[mstem]

.002 BC gap? The hot Dan Wesson's BC gap are .002. They are some of the most accurate handguns on the planet. Yes, they have to be cleaned more often but I clean mine after each shooting session anyway so that's a non-issue. Be happy you got a gun put together that tight.

 

[Zipdog]

Too much measuring not enough shooting.

 

[KLYDE]

Every revolver I've had rehabbed and tuned at the Performance Center has come back with .003 B/C gap. Shoot it and don't worry.

 

[H Richard]

I'd recommend shooting mostly jacketed ammo as you will have less cylinder front build-up than with lead ammo. It will eventually develop a little bigger gap after enough use. You already know ti keep it clean for reliability. Have fun, it should be a great shooter.

 

[zach_c]

I put 50 rounds of 38's and 8 rounds of 357's this afternoon over a short period of time, including putting two dozen 38's thru as fast as reasonable towards the end of shooting. I didn't notice any issues with binding. The accuracy could be better, but I assume that was me.

It's amazing the knowledge folks have with this stuff. I appreciate all the suggestions and will keep in them in mind as I get to know this gun. Thanks.

 

[wolverine]

Morning zach_c;

As long as you are shooting low power loads or jacketed loads then that .002" gap probably won't be an issue.

Tight cyl to barrel extension issues usually start showing up when shooting lead bullets at decent velocities when the front of cylinder/rear of forcing cone starts leading up a bit.

With the amount of lead I shoot (personally) I can't get by with that tight of a cyl to barrel gap on any of my S&W's, but I shoot a lot of rounds at one range time, & only clean when re-storing the gun.

Just keep shooting it with lots of different bullet configurations. If it doesn't get tight with what you are shooting, or how you are using it, then you are good-to-go.
If it starts binding up then you might have to limit your ammo choice or have Smith address it.