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Old May 7, 2013, 01:24 PM   #7
Unclenick
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Join Date: March 4, 2005
Location: Ohio
Posts: 21,013
I've only had it make a really apparent difference once. Back about '92-'94 somewhere, I decided to try shooting 2520 in an M1A under 168 grain SMK's. With the stick powders I'd used I had always been able to tune in moderate loads to about 0.75 moa at 100 yards in that gun. But with 2520, about 1.25 moa is all it would do for me. By coincidence, I'd just got my first deburring tool around that time, so on a whim, I decided to try it. Immediately the groups shrank to about 0.75 moa. I got all excited. I figured that if it cut 40% off those groups, it would do the same for the stick powder groups. Nope. Didn't do anything for them. No amount of retuning did either. The sticks just didn't seem to care one way or the other in that gun.

Looking back twenty years later, I think there were two reasons it mattered. One is that I was using Federal 210M primers then, being blissfully unaware of the slamfire issue at the time. Second, the moderate load didn't fill the case at all well. I strongly suspect (though I have no interest in financing the experiment to prove it) that I simply needed a magnum primer both because spherical powders generally like a little extra ignition enthusiasm, and because of needing to better pressurize the empty space. By deburring the flash hole I had enabled a mild primer to perform just enough better to light the loose load of spherical powder more consistently. But with the right primer there's a good chance it would have made no difference.
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