I'm building up a .300 WSM on a T3. I just got a HCA mag, and it doesn't want to drop out of either factory bottom metals that I have. It's a pretty tight fit, to the point that it's a royal pain to pull it out. I'm sure I can fix this by lightly sanding the insde edges of the BM, but I've been toying with the idea of using one of the aftermarket offerings. I would prefer to go with the best functioning option, if there is such a thing. Anyone care to comment?