Headspace determines primer appearance. The primer always comes out first before being reseated by brass expansion. Look at a straight wall revolver case. Headspace is not at the shoulders since there is none. It is the distance from the case head to the recoil plate. Every single .44 mag can have a dead flat primer well within pressure limits. The force from the flash hole will send a hammer back to near full cock. The squirt from that hole can be horrendous well before peak. To rivet a primer as shown means headspace was excessive by full length sizing too much. It has nothing to do with final pressures.
Fed is supposed to be weaker but I have taken Fed 150 primers to near 60,000 # in the .454 with cut down .460 brass without a flat primer. I tested the 150 to the .500 S&W but the 155 was more accurate and my go to from the .475 up. The 150 is the only for the .44 mag.
Weatherby had ignition problems at the start. Fed was the first to make a mag LR primer that brought the Weatherby to life.
