Mod 18-4 Misfires

[ggross]

Thanks for the spring/screw comments (a few of you)! I removed the spring screw and the end had been filed! Don't know how much is missing so I'll get a new spring/screw and go from there.

 

[Jim Watson]

When I have had ignition problems with S&W .22s problem is solved by going with a Wolff mainspring (also make sure the strain screw has not been modified). The Wolff springs are IMHO a better design for rimfire.

The problem I found with the Wolff Power Rib mainspring is that the strain screw enters the groove and reduces preload by the depth of the groove, just like backing out or shortening the screw. I went back to the stock spring in my .22. I have a primer cup shim in my .45.

The next time I want to mess with springs, I have a Wilson set, no groove.

 

[crankyoldlady]

You don't indicate if you are shooting single or double action.

 

[ggross]

In my very first post I indicate that it happens in both SA and DA.

 

[3rdgeargrndrr]

Thumbs way down for not showing a picture.
I think its also ammo related. A new box/ different ammo just to double check.
In California, I would give you a couple of 22’s of various brands but that would mean a BACKGROUND check to transfer ammunition first. Sorry. Had to rant a little.

 

[crankyoldlady]

In my very first post I indicate that it happens in both SA and DA.

So you did. Sorry.

You might experiment with a shim under the strain screw to see if it makes a difference.

 

[ggross]

So you did. Sorry.

You might experiment with a shim under the strain screw to see if it makes a difference.

I did that yesterday and will see on Tuesday at the range if it makes a difference. Have a new spring/screw on order in the meantime.

 

[Hair Trigger]

Maybe it’s normal but that firing pin strike seems a long way from the edge of the case rim.

That looks pretty normal to me, a round pin seems to center a little further in than a flat one, which will extend to the edge of the rim.

Be sure the chambers are clean and ammo is seating fully - if not, the first hammer hit moves the case and the second time around it fires.

Yes, try this. My M48-4 (.22 Magnum) does the same as yours, if the cylinder gets dirty enough and residue doesn't let the cases seat firmly in the chambers. I start out with a clean gun and get no misfires until maybe the 4th or 5th cylinder load, then begin seeing the occasional failure to fire. If I leave the cartridge in the same position and rotate the cylinder back around and strike it a second time, it invariably fires, and it's striking the same spot on the rim. Looking at the initial strike, it doesn't appear different from the ones that have fired. If I stop shooting and clean the cylinder with a bore brush and swab, paying attention to the case head recess, it starts shooting well again. The chambers of my revolver seem a bit snug, doesn't take much to make the cartridges fit tightly.

 

[ggross]

I did that yesterday and will see on Tuesday at the range if it makes a difference. Have a new spring/screw on order in the meantime.

The shim worked so I think the filed Strain Screw was the problem. I backed it off a few times at the range and got misfires. Tightening it back up and there were no misfires. The replacement screw and spring are on the way and I think that will solve the problem once and for all.
Thanks to all who provided your expertise!