I think you are screwing the seating die down to far. Turn it back AT least 1 full turn or 2 . Then use the steam to run it down to seat your bullet. MY guess is you die has build in crimp and its crimping AS it seats the bullet. THIS may becausing it to BULGE you neck. Back it of a round or 2 and try it again
Well I did this and it worked perfect for the 243 I couldn't ask for it to chamber anymore perfect than it did. The 7mm mag tho was a different story I still have the same issue of the bolt handle being difficult to lift and lock down. This is all after backing my die off 2 turns and putting the bullet my friend made and setting the seating stem by it.
