Quote:
Originally Posted by bandit1250
I believe tuning the shape of the firing pin profile is one of the best things you can do to eliminate miss fires and help improve accuracy even with some lower grade ammo.
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Done right, it absolutely helps. Done wrong, I've found it can actually destroy accuracy.
I started FP shape testing with a shallow wedge shape attributed to Bill Calfee. It made a huge improvement in reliability, but accuracy tanked. I believe it only worked for Bill because he uses match chambers and mine are sporting. So I went thru several shapes before determining what works best.
A Ruger Mark3 was my test bed (and made the hits in the photo).
1) Whatever FP surface hits the brass should be parallel to the breech. Any tipping of the surface will destroy accuracy.
2) The FP strike should be far enough inside the thick outer brass ring so it doesn't alter it's shape. If the strike is compressing the ring, or bending it outward - the strike is being slowed and will be less effective. You shouldn't be able to tell where the strike occurred when viewing the brass from the front or side.
3) The strike needs to be close enough to the thick brass ring to allow the priming pocket to collapse as the FP tip passes by. You're basically folding brass over the priming and stretching it into the pocket. A strike too far inside the ring will fold the brass, but not stretch it into place against the anvil. See the pic with arrows pointing to the anvils of CF and RF primers.
Now you should see the real problem with rimfire reliability: the anvil is at an angle to the FP strike & is protected by the thick outer ring. A slow strike can push the priming mix out of the pocket & into the powder chamber. A FP hit further in will be faster and will capture at least most of the priming mix. That capture action is where you make huge gains in reliability.
Thanks for all the nice comments. I hope this helps encourage you to try FP shaping. It's no replacement for cleaning your gun, etc. But it has helped to improve my misfire rate to well below 1/10,000 rounds. I doubt I've fired 10,000 centerfire rounds in my life, so rimfire ammo now appears to be just as reliable. YMMV.