On the left is the follower from a 10rnd MDT 308 mag, on the right is the follower from a 10rnd MDT 6BR mag. The 6BR follower is about twice the height of the standard follower. Seems this is the root of the issue right here.
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Removing the base plate and loading 10 rounds into the mag and placing the follower on top shows very clearly that the follower is too tall. More than half of the follower stick out beyond the bottom of the mag! This means the follower is bottoming out long before you get 10 rounds in there, and the only way to make room for the remainder is for the cases to pack more tightly together and bulge the mag walls.
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Like I said, with mine I am able to load 5-7 rounds before it starts getting very difficult. In order to get all 10 rounds in there it's a battle between the brass and the steel mag walls. The mag wall will give a little, but in the end, it wins the fight and your brass ends up getting hammered.
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