Mike0231 has a great illustration of not so right and the one on the right that is done right. Also insure that the case expansion done for seating is removed with a taper crimp die. You can pinch the round between thumb and forefinger the case should be a continuous taper from the head to the case mouth the belling should be gone.How much of the front driving band is sticking out of the cartridge case mouth? I have seen this happen several times. barrels with a long lead can be a problem if the bullet engages the taper before full battery is achieved. Those shooting "blue" bullets in Glocks "run and gun" where a bunch of rounds are fired rapidly. The chamber heats up enough to melt the blue paint, when the barrel cools, the bullet is glued into the barrel lead thus locking up the action. Seating the bullets in the case .010 deeper usually fixes the issue.