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Posted: 3/20/2016 2:17:20 PM EDT
| I loaded up some 77gr Sierra TMK's to test out with AR Comp powder using once fired, annealed, LC brass with CCI No. 41 primers. OAl was 2.260. Loads were 20 gr, 21gr and 22gr. Of the 5 rounds i loaded for each charge weight, i had 1 primer backed out for 21 gr and 1 primer back out for 22grs. Velocity was 2441fps with the 22gr (chrono issues preventing me getting any good data from the other loads). Ive run 24gr of varget with the same other parameters without issue. Whats causing the primer backing out? Ive heard that it could be low pressure but i thought i was at the higher end of the pressure spectrum with these powder charges. |
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Primers will back out often with lighter loads.
Fact is primers back out more often then most people realize. The case expands initially and grabs the chamber wall. As pressure rises the primer backs out the amount of space between the case head space and the chamber head space. Most of the time the grip of the case to the chamber wall is overcome by the pressure and the casing backs up against the bolt face. With lighter loads this often does not occur so you end up with backed out primers. Guys (like me) who shoot reduced loads using cast bullets see backed out primers all the time because many of our loads never reach high enough pressure to break the casing to chamber hold of the initial expansion. Motor |
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"Backed out" meaning raised slightly above flush with the case head? Or "Backed out" meaning they left the case entirely?
Resizing your brass too much and using light loads can cause primers to sit higher than flush. Primers completely gone fro the case means excessive pressure or brass that has been reloaded too many times. |
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Quoted:
"Backed out" meaning raised slightly above flush with the case head? Or "Backed out" meaning they left the case entirely? Resizing your brass too much and using light loads can cause primers to sit higher than flush. Primers completely gone fro the case means excessive pressure or brass that has been reloaded too many times. here is a picture. i believe the max load is 22.1 grains so its not a light load. Its now twice fired brass. Hand primed it so it wasnt a sloppy primer pocket. 
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