Re: question for the experts, or anyone else who has an answer
Okay, I have not loaded 270 in a long time. But, I do use R22 in a 25'06AI. Your load, I'm not looking it up, but it just sounds hot, to me? What you are describing, again (to me) sounds like case head separation. If you do, you have an unsafe condition and you had better get to the bottom of it before you leave the case body stuck in the chamber while removing the rim. A competent gunsmith can fix this for you.
But somebody else mentioned a possibility, misalignment, probably caused by a severe overload, bulging the chamber. Every round subsequent, will show a bulge conforming to the damaged chamber. There is only one solution, if you have enough barrel; cut a new chamber. Otherwise, it will make a good jack handle.
Good hunting. LB