Just been firing my first lot of handloaded .243 ammo. Part of round development process to get optimum seating depth. Had 3 batches (4 rounds in each batch) of ammo: One batch just touching lands, one seated into the lands and one batch off the lands. I forget the exact measurements. (Don't worry, I got them written down!).
All cases were Hornady once fired (saved up from factory ammo).
Bullets were 80gn Noslers.
Powder was 37.5 gns of vitavari N140
Rifle is P-H Safari Deluxe.
When fired, almost all of the cases blew out on the base at the point where there's a slot in the bolt head where the retaining catch runs through. At this small point the case base is unsupported. In some cases there was just a small raised rectangle of brass at that point, but in others it had blown out enough to crack and allow combustion gases through, which have caused burns on the outside of the case (around the primer hole) and some minor pitting on the bolt face.
The rounds that were seated off the lands were perhaps the worst, with all of them affected to some degree, and 3 out of the 4 having blown right through, but not sure if this is significant. (This was also the batch with the best grouping!).
What's going on here?