Thread: Overpressure signs on Belted Mag

Originally Posted by Tankd

Looking at the numbers of your drawing and your cases it looks like you may be sizing your cases to much . By sizing to much it causes the case to try and fill the gap more giving a false impression .
The drawing is for a case that is meant to fit "All"" chambers , and the first two are smaller than the specifications, which means they could be to small for your chamber causing issues and the other shows expansion of .001" showing expansion but no issues with extraction . Chamber specs. are here https://saami.wpengine.com/wp-conten...sting-Copy.pdf.
Go back to the beginning and start again remembering that load data is inherently conservative but not something to be ignored or reckless with ,it maybe that you are at maximum powder but that your sizing of the cases is clouding what is happening?.

To Clarify i fired about 20 rounds and only the heaviest loads showed this deformation, the drawing is just the Sammi case drawing and i was just using it to show where i was measuring the cases "webbing in front of the belt" after they had been fired - looking for excessive expansion that would suggest over pressure.
As an example the two types of off the the self unfired ammo i have measured is 12.98mm on average at that location and after sizing in the die i'm getting 13.00mm +/-0.01

After reading bunji's great link - I note it was brand new powder and a very hot day at the range which also may have contributed.

i suppose it was just a bit unexpected as a lot of others on this forum have commented they use loads of over 71gns of AR2217 with a 7mmRM & 162gn projectile.