Re: rookie dealing with possible pressure signs
I've seen similar results when I attempted to seat long bullets (VLD's, etc) to magazine capacity in large/belted magnums. In other words, a load that normally showed no pressure signs when seated to lands or jumped slightly has cratered shell casings when the bullet base was seated below the neck junction. Obviously deeper seating creates more neck tension and greater friction, therefore greater pressures. But typically you will experience sticky bolt lift, cratered or loose primers, or other pressure signs as well. My advice would be to start with lower charge weights and work up in .5-1 grain increments while watching for pressure indications. Keep in mind that just because a load shoots well from my rifle, it may not be safe in yours due to faster twist, tighter headspacing, etc. And primer selection, seating depth, neck tension, etc. can cause large increases in pressure within loads.