by BD1 » Mon Jan 11, 2010 5:50 pm
I thought about the following for a few days before posting it, but decided to go ahead.
Another reason that I decided to section these two cases:
The case on the left has been loaded, side crimped and fired ONE time only. Case on the right has been loaded, side crimped and fired TEN times. I have some concern that continued use of the side crimp may eventually result in case failure at the side crimp, somehow leaving a ring of brass from the failed case mouth in the chamber. If the subsequent round was able to chamber by driving this ring forward into the throat, an overpressure condition could result.
The results of sectioning these two cases has eased my mind somewhat. I do not see any signs that the side crimp is significantly weakening the case on the right. The brass is stretching out a bit from the repeated side crimp, but there is no sign of the thinning groove that would indicate incipient case failure. I will section another case at 20 loadings to check this again. My hope is that cases will last at least 20 loadings. This is entirely possible at 40,000 psi if the loading procedure does not add any significant stress risers to the case.
A caveat: One case can not tell the whole tale. My plan is to shoot a "batch" of twenty cases another 10 loadings, and then section the whole bunch to set my mind at ease on this issue.
Second caveat: Brass flow is much more pronounced at higher pressures. Getting near 60,000 psi some lots of brass will move significantly. So taking comfort from multiple loadings at 40,000 psi will not save your bolt, or your face, if you choose to push the pressure limits for multiple loadings.
BD