Light primer hit M17

[oldRoger]

I have a new to me, M17-4, Catalog says 1983, it’s in beautiful condition, I would say 98%, I am having ignition problems. Usually one out of 6, or sometimes two will not fire, hard to say if the firing pin indent is lighter or not on the unfired rounds, If I turn them and try again most will fire. If I put the FTF rds in my M63 they all go bang.
I have not tried a lot of brands yet, clearly some is worse than others. Mainspring tension screw is as tight as it will go.
Any suggestions? I have ordered a Wolff mainspring.

 

[oldRoger]

I have a new to me, M17-4, Catalog says 1983, it’s in beautiful condition, I would say 98%, I am having ignition problems. Usually one out of 6, or sometimes two will not fire, hard to say if the firing pin indent is lighter or not on the unfired rounds, If I turn them and try again most will fire. If I put the FTF rds in my M63 they all go bang.
I have not tried a lot of brands yet, clearly some is worse than others. Mainspring tension screw is as tight as it will go.
Any suggestions? I have ordered a Wolff mainspring.

 

[bountyhunter]

Is it the stock mainspring?

If it's used, somebody may have done a trigger job and ground the end off the strain screw. If the DA pull is in the 8 - 9# range (or less), it has been lightened.

You can probably fix the light strikes by bending the mainspring a shade flatter. If the strain screw has been shortened, a a new spring alone may not fix the problem. You also need a new screw.

 

[Gun 4 Fun]

Make sure the recesses for the case rims are clean and allowing the cases to fully seat. If they are held away from the bottom of the recesses a little bit, it'll cause light strikes, since some of the force of the hammer and pin will be used to fully seat the cartridges.

.22's leave a lot of residue normally anyway, and K-22's have tight match chambers, so it doesn't take much to foul things up. Just something to check.

 

[oldRoger]

More information, I took ten rounds each of CCI Stan. Velocity & Lapua Master M and fire them in the M17-4. I have been shooting these two lots for some time they have been 100%. Seven of the CCI fired first hit, I turned the other three 180 and tried again, two on the second hit, the last one fired on the third hit. The Lapua fired 10 for 10.
I do not know if it has the original spring. The cylinder is clean as could be. In fact the gun looks practically new. The strain screw looks full length. I don’t have another one to mike.
It seems to me that it is a very near thing. The new spring should be here soon. If that doesn’t work is it possible to get a longer firing pin?

 

[john traveler]

The usual reason for rimfire misfires is gummed up oil in the firing pin recess, dirt under the extractor star or rim recesses, or excessive cylinder endshake. Since your examination does not show a shortened strain screw, a weakened mainspring is the most likely item.

It's not likely you can get a longer firing pin, since the rimfire system requires the fp not strike the chamber rim when you dryfire. It's still possible you have a gummed-up fp. Try dripping solvent into the fp channel and manuall pressing the fp in and out several times. You can also cycle the action using your off hand to cushion and prevent hard hammer impact on the fp. Do this a few dozen times to work the solvent in where it will do the most good.