#1
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Cooper M38 firing pin fit
What would the proper fit be for the firing pin to firing pin hole in the boltface be?
My Cooper M38 17AH, which has given me fits since day 1 for piercing and cratering, measures out to:
Thanks, John |
#2
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Do you have a set of number drills? If so, try inserting the back of the drill to use it as a pin gauge or to measure the next closest size.
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#3
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No number drills, but I do have a whole box full of "misc" bits I "inherited" from my grandpa! Next closest size is .077 and it did not fit...
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#4
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I have had the same problem with my Cooper 38's (3) & had Greg Tannel bush them all. Unfortunately, the Cooper firing pin is case hardened, so when Greg turns it down to .062, it loses it's hardness & hence stiffness, so it wants to bend. Because of this problem cropping up, Greg won't do Coopers, and a number of others, right now. He is planning to get some CNC screw machines that he already has, programmed to make the various firing pins out of heat treated 4340, I think he said. No matter, can't get it done right now. The Coopers seem to have quite a bit of firing pin energy, even with their short pin fall, so I would recommend trying primers with thicker cups if possible.
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#5
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I have wanted to get the bolt face bushed but did see on Greg's website that he doesn't do Coopers.
I have tried all the primers available in my area, to include: CCI BR4, CCI400, CCI450, WSR, Rem 7 1/2, Rem 6 1/2, Fed 205, Fed GM205M. I am getting these issues with loads that should in no way crater or pierce, ie 11.0 and 11.5 N120, 1680, and higher too. Heck, I have even gotten good craters with a no bullet-Bullseye fireform load... |
#6
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Talk to Greg & see if he'll do a run of Cooper firing pins, or maybe Dave Kiff.
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