How far should the firing pin on a J frame 640 protrude, trigger fully to rear? I range tested it after it had not been fired in a few years. Getting intermittent FTF from light strikes in the center of primers. Seemed maybe worse when I deliberately pulled thru slower. No history of issues. I know it could be several things but I would like to know about firing pin protrusion. I read .055" on this. Of course I will investigate hammer spring, possible debris in firing pin channel etc. but I would also want to know if this is a factor. I measured the gap between this firing pin and the back of the cylinder with a feeler gage and it also looks like it is a few thousanths larger gap than on a K frame. IF that means anything.
J Frame (640) Firing Pin
- Thread starter tom2
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Have you checked the strain screw for tightness?
rincar
Member
The Model 640 does not have a strain screw. They have a coil main spring. As far as light strikes go. I would try different brands of ammo. Until I found a brand that would fire consistently. Also clean the internals real good
In terms of protrusion figures, the Kuhnhausen manual lists the frame mounted firing pin protrusion as ".050" minimum, .055" min is better, .062" maximum." (5th edition, page 198)
jjmIII_Ruger
Member
Look up the spring kit from Apex. It is a bargain and includes hammer and trigger springs. Also new firing pin and spring. Did a 442 and 640 and both came out great.
All that is useful info. Right now I am trying to find my box of gun parts that I have not seen since I moved. I believe their is an OEM hammer spring in that lot. As soon as I find that I will open er up and clean relube, blast out the firing pin channel, I think it is pinned in. All the light strikes fired on the second try. OK on the 55 thousandths being medium protrusion. I looked in my Jerry K Smith book and could not find that spec for some reason. But my copy is falling apart now! A new full power hammer spring is going in one way or another, with that little concealed hammer I want all the oomph as reliability is #1 with this particular gun, it is not just a range queen.
Found my gun parts. Took 640 apart. Blasted cleaner thru firing pin hole even though it appeared to travel to stop. Took out hammer spring. It was about 1/8 shorter than a factory Cheifs Special spring I had. Probably a Wolff spring. Relubed parts and installed OEM spring. Now pull is still smooth but heavier than it was before. Hope this does it. Might be bad news to mess with the OEM weight spring in these due to the small low mass hammer etc. More critical than in my K frames, which actually have improved pulls but unaltered OEM hammer springs. And no issues. 640 is early or mid 90s vintage.
Sounds like you're implying that you might of had a reduced power mainspring in it?
An OEM mainspring is the safest way to go but I've had good success with APEX's spring kit for the J-frame.
A longer firing pin, which is included with their kit, is key, I believe, to making their combination work.
Have you measured your firing pin?
Also, any increase in endshake your revolver has gotten will exacerbate a short firing pin.
.
An OEM mainspring is the safest way to go but I've had good success with APEX's spring kit for the J-frame.
A longer firing pin, which is included with their kit, is key, I believe, to making their combination work.
Have you measured your firing pin?
Also, any increase in endshake your revolver has gotten will exacerbate a short firing pin.
.
Yea well my original inquiry about firing pin protrusion garnered the response that at 55 thousandths it is nominal. Apparently I must have put in a Wolff spring years ago to make the DAO a bit easier to cope with. And it was never having issues in the past. I tried the Wolff leaf hammer spring in a K frame once and did not like it, had pushoff and was incredibly light pull but now my Smith K frames have a trigger return spring that is the weight choice just below OEM as lighter results in weak return, no good except for target use and I have OEM leafs in K and L frames. I did not have a variety of ammo to use at the range. I had some old stuff and the range is out of .38 ammo. But weak hits with ANY kind of ammo is bad news and I will suffer the heavier spring in the J frame for absolute bang every time. The gun has no endshake issue and is very tight. And being steel frame, .38 only, and low round count, should stay that way. I guess it is a warning to anyone with the internal hammer J frames that you don't really want to mess with the springs in the case it is a gun with a real purpose.
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Model 640-Light strikes
Had a similar issue with my 649. Previous owner slicked up the action and apparently installed lighter springs. Installed OEM main and 14# rebound spring. Trigger pull is heavier, but smooth. No more light strikes.
Had a similar issue with my 649. Previous owner slicked up the action and apparently installed lighter springs. Installed OEM main and 14# rebound spring. Trigger pull is heavier, but smooth. No more light strikes.
