S&W 65 Double Action Misfires...

[Southern Raider]

I have a S&W 65 that occasionally misfires when used in DA. In SA, all rounds have gone off without issue. What should I be looking for here?

• The mainspring is a new Wolff standard power (Type 1 Power Rib Mainspring).
• Firing pin protrusion looks OK, but I don't know the specs for protrusion or the space between the rear of the cylinder and the back of the frame.
• In DA, the hammer falls from a point that is not as far back as from where it falls in SA. This should be normal to a degree. Do the DA sears ever wear to the point where this problem happens?

Anyone have some suggestions for quantifiable things to check?

 

[Bullet Bob]

At the bottom of the front gripstrap is a screw that rests against the mainspring. Make sure it's screwed in flush with the gripstrap,

 

[gunfan]

Bob beat me to it. If the problem persists, take it to a gunsmith, and have the double action part of the sear checked.

Scott

 

[Southern Raider]

At the bottom of the front gripstrap is a screw that rests against the mainspring. Make sure it's screwed in flush with the gripstrap,

Flush and tight it is.

 

[tg_26101]

put the factory mainspring back in

 

[Old Fuff]

On all revolvers the double action release point is earlier then the single action let-off. Some release sooner, but Smith & Wesson's release later because of the way their lockwork is designed.

You might have some cylinder end-play, or "shake." Using automotive shim gages, measure the distance from the back of the cylinder to the breechface, while holding the cylinder backwards as far as you can. Then make the same measurement while pushing the cylinder forward in the same manner. Subtract the first measurement from the second, and the answer should equal the cylinder's end shake. More then .003" could explain your problem. It is possible that your "standard" aftermarket mainspring isn't truly the same as a factory spring. Also remove the mainspring strain screw (mentioned in previous post) and look at the end to see that it's blued and not bright (indicating that it might have been shortened.)

Last but not least, be sure the internals are clean and lightly lubricated.

 

[Southern Raider]

OK, the rear measurements range from 0.063" to 0.067", with a corresponding front gap of 0.004" to 0.008". Firing pin protrusion is about 0.042".

Power Custom makes small shims to remove end-play. Is that the correct product to use in this case?
http://www.powercustom.com/parts_bearings.htm#Endshake

 

[frankt]

Yes, I had a model 10 doing the exact same thing. I could reload with federal primers and the gun would fire 100% of the time. With cci primers that worked in all my other guns the model 10 would missfire 3 out of 10 times.

I added a .002 shim and it now fires with all ammo. It is surely worth a try in yours also.

 

[Old Fuff]

From the measurements you have given I presume that this revolver does not have a cylinder where the case heads are recessed into the chambers. If I am wrong, correct me and disregard anything that follows.

Headspace (the distance between the back of the cylinder and the front of the breechface) should be .060” (go) to .064” (no-go). At .067 your revolver is out of tolerance and apparently has a maximum endshake condition equal to about .004” as indicated by the cylinder gap measurements. The Powers bearings are one way to correct the condition, and in my view, the best one. There is however more to it then simply adding some bearings (I call them “washers” ) and so I will go into a more detailed post when I have more time.

While cylinder end-shake is part of your problem, it may not be all of it, because with a .042” firing pin protrusion I would expect the cartridges would fire even though the headspace is apparently excessive. So you may have to correct the headspace issue, and possibly replace the mainspring, and/or the strain screw too, but it’s too early to tell at this point.

 

[Southern Raider]

Old Fuff,
Thanks for all the help to date. I'm finding revolvers to be deceptively much more complex than they first appear to be.

The cylinder does not have recessed case heads, so your advice is spot on, and I'm sure we all look forward to some more pointers on installing the shims. I'm guessing that these go at the front of the cylinder, which should also have the benefit of pushing the cylinder rearward and closing up the headspace at the expense of increasing barrel-cylinder gap.

On firing pin protrusion...I found this checklist from the American Pistolsmith Guild, which indicates:

Smith and Wesson hammer nose/firing pins should protrude a minimum of .045" to .060".

http://www.americanpistol.com/Pistolsmiths/swchecksheet.html

If these numbers are correct, it would indicate that my firing pin is a bit short as well, but that is contrary to your comments.

 

[Old Fuff]

This will be a short reply because I'm pushed for time. More will come later.

Revolvers and pistols are both complex, but each in their own way. Your problem I think, is somewhat like a car that has a lot of hard miles on it and really needs a good overall tune-up. Fortunately that isn't particularly expensive, but buying the special tools that are sometimes needed can be. That's why you'll need to decide if you want to do the work yourself, or send the gun to a professional gunsmith or Smith's service department. Be that as it may, The High Road will insure you make an informed decision.

Yes, I know that the pin is short, but not so short that I'd expect misfires. However a combination of cylinder end-shake, a short pin, and a light mainspring or short strain screw could easily explain what is happening.

But sep-by-step we'll get to the bottom of it.