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Old December 29, 2019, 02:46 PM   #191
P Flados
Senior Member
Join Date: January 8, 2017
Location: Wilmington NC
Posts: 115
As I recall, Mehavey's chamber neck is on the big side (it can chamber loads with 0.358" bullets), but the throat is tight and/or short (correct me if I am wrong).

Is there any chance that a previous round had left a ring of lead (shaved off) at the step just in front of the case. I have seen this quite a bit on a 9mm Glock that I load for. If there was lead ring and then a full length round is jammed into the chamber, I could see the lead ring being pushed inward and up against the bullet (again this does happen on the Glock) . This would tend to hold the bullet in place more than normal. This could have elevated your "start pressure" for the one round that had the pressure spike consistent with what you seem to have figured out from QL.

For Stagpanther, he was using new brass. At times, I have had new brass act very "sticky" and require much more than normal force to to expand the brass and/or have high/inconsistent seating force. If his one bad round just happened to "stick" to his jacketed bullet, again it would cause an elevated start pressure.

For both events, there seems to have been a substantial pressure excursion when compared to similar rounds that did OK. When I try to come up with some explanation for a big pressure increase with no increase in powder and no change in components, there are not a lot of choices. The initial breakaway force needed to move the bullet seems to be the least unlikely at this point.
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