Light Firing Pin Strikes

[Seven High]

Would someone please tell me what the cause of light firing pin strikes are on an older Smith K frame. They occur intermittently when shooting factory and handloads. The main spring has been replaced. The internals have been lubed.

 

[45fan]

Not sure about the K frame specifically, but I know that the J frame has firing pin issues from some years being too short. Could be the same issue in the big brother as well. I know that was the fix for my 442 that was having intermittent misfires.

 

[PGRChaplain]

From the S&W Forum; "I've had this occur on a number of my own S&W revolvers. Typically it has been resolved by checking the strain screw and making sure it is tight to the frame.

Look in the Kuhnhausen book or others for parts description. It is easy to access the strain screw: take off the grip. The screw at the bottom of the hammer spring at the front of the grip frame is the strain screw. Sometimes they will back out 1/8 or 1/4 turn, which takes a little pressure off the spring, resulting in unpredictable light strikes.

By the time they are backed out 1/2-1 turn, misfires are frequent.

You will know very soon whether this is the cause. If there is _any_ play at all in that screw, I will get what you are reporting. If this solves the problem, I'm told the wonders of blue loctite will resolve it. Blue not red".

 

[Bosshoss]

There are many things that can cause this. You said the mainspring was replaced. Was it replaced with a stock one or a reduced power spring? If the strain screw is tight check and see if someone shortened the screw. Some file or grind the length of the screw down to lessen the tension on the mainspring and reduce the trigger pull weight. A easy way to test this is to take a FIRED primer and remove the anvil (guts). loosen the strain screw and slip the primer cup over the end of the screw and tighten. This will last long enough to test the gun and see if you need a longer screw.
Make sure there is no dirt under the extractor star and the chambers are clean and the rounds are seated all the way in. Dirty chambers can hold the rounds up slightly and the hammer just pushes the rounds into the cylinder instead of setting off the primers.
Also check endplay, excessive endplay in the cylinder will cause this. Endplay is checked with the cylinder closed and empty. It is how much the cylinder will move fore and aft. You want .001 -.003 any more than that and misfires can start creeping in and it can get bad enough that the cylinder rubs on the barrel.
There are lots of other things that cause misfires in a revolver but those are the main ones that I see.

 

[sloughfoot]

Cylinder end shake and a too light hammer spring. Sometimes timing. I have moved totally away from "trigger jobs" in S&W revolvers. I go for smooth but with stock springs.

Use a pencil. If your gun doesn't stick a pencil in the sheet rock in the ceiling, the hammer spring is too light.