Well, It's like this. With the heavy walled 284 cases and a tapper crimp, everything conforms to the outside specs. When the round is slamed into the chamber from a mag the bullet jumps forward. The base being slightly larger due to the tapper crimp, expands the case mouth and acts like a wedge anchor.
Pulling it out from the base using the charging handle only makes it tighter! The only way to get it out is to drop a cleaning rod down the barrel with the bolt unlocked to back the bullet up and the case will just drop out. Very scary!! With the bolt unlocked the firing pin is not long enough to hit the primer. Still, Very scary! Look at my post on "Stuck cases".
Inside reaming of the 284 cases helps, with the side crimp it eliminates it.
Try them with a Dummy round first!