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Johann the Horrible

Blown Primers

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I have been reloading for about 26 years. A few weeks ago I bought a new M&P 9L and almost immediately ran into problems. The 9mm Minor load I developed for my CZ just would not fire in the M&P. It seemed like light strikes initially but after "de-oiling" the striker and tunnel it seemed to go a little better, but only a little. Eventually I found that my rounds were a tad to long for the Smith so the energy of the striker was used up to try and seat it further. So I shortened the rounds by a fraction and immediately things seemed to go a lot better. The rounds felt "softer" than in the CZ and everything flew until a primer blew out of a case and caused a 5 second stoppage. OK so a blown primer sometimes happens and stuff like that is part and parcel of IPSA. I found both the primer as well as the case and the primer pocket seemed to be a bit oval. The primer itself seemed quite normal. All the other cases and primers seemed quite normal. On the next stage I had another blown primer and on the stage after that two. I withdrew my ammo from the match before I got told to do so and completed the match with military stuff I had in my car for such emergencies. The military stuff felt a lot "hotter" and accuracy definitely suffered. No further blown primers or problems except for a Mike on a far target.

The load I developed over the years, and that helped me get into the Provincial, team consists of a 137gr lead bullet in front of a few grains of very fast propellant. The load factored about 137 out of the CZ and 148 out of the Smith. Considering that the Smiths barrel is a bit longer it is not very surprising that I am factoring higher though I did not expect such a big difference. The reason I do not mention the propellant is that it is South African and thus not well known in the USA(S121). Now 1080ft/sek is quite "hot" for a 9mmP but not overly so. In my stupid youth I did manage to blow a gun or two and the blown primers on Saturday definitely did not feel the same. I examined the gun minutely and found no reason in the gun for the blown primers. The cases are of mixed heritage, mostly PMP once fired. Obviously the problem lies in my ammo since factory ammo seems to run quite well in the gun. I have "de- mothballed" the CZ and it runs on my ammo without a hiccup feeling a lot "hotter" than the Smith. Except for overloading can any of you think of a reason why I should be blowing primers out of my new gun. I would hate to mothball the Smith but as we are shooting a big match next Saturday I need to a gun/ammo combination that works on the day.

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Check the reloads primer depth. Compare the depth with the stuff that runs. If you can post a pic too.

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Sounds like you're pushing the pressure envelope with that powder judging by the (pretty massive) increase in PF with what you said was a small decrease in OAL, which is what caused the primers to exit, stage right. I doubt your M&P's barrel is that much faster than your CZ's.

Measure a round and then chamber it a couple times and check for a reduction in OAL to see if you're also getting setback, which would contribute to the pressure problems.

You probably need a slower powder.

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taking a wild guess here, i would say that the CZ has a more 'generous' chamber than the M&P, given thatthe rounds were long in the M&P but ran in the CZ...not knowing the powder charge, but sinking the overall length even by 3 thou. can and does in some cases double chamber pressures, your not working with a whole lot of case capacity in the 9mm...might be time to make some more that is a half to a full gr. below what you already have????

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Rather than a headspace problem it may be a freebore problem. You did not mention what your initial OAL was or what you shortened it to. The bullets might have been hitting the lands in the barrel and keeping the cartridge from chambering completely and that was what was keeping it from firing at first.

Brian

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M&Ps don't like long ammo. I shortened my loads to 1.120" and chrono at that length to avoid bullets hitting the leade.

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