I was under the impression that the HPT process was basically subjecting the bolt to a proof test, which also has the effect of potentially shortening the overall life of the bolt by quite a margin. I read that the US army found that bolts (even HPT/MPI tested) will begin to crack at 5,000 rounds, and will generally break at 10,000 rounds.
If bolts tend to let go at the same time, I'm not sure if the benefits of HPT stack up, but interested in others views.
Bookmarks