Quote Originally Posted by SEshooter View Post
It sounds like you need more spring tension or the feed lips to be adjusted. Is the long action mag box for a round of the same case diameter as the 243? (ie: 30-06, 270, 280, etc.) Maybe put a piece of wood in the bottom of the mag with the spring on top. You may lose 1 round in capacity though but it is easy to return to normal and it will let you know if spring tension is the problem.
Good idea for a temporary fix, I'll try that. Mag box is for the 270 Win.