Knowing I'd eventually turn to a Dasher from a Creedmoor when I started loading my own ammo I got some mags awhile ago which I finally set up and shot last weekend. I had the hardest time trying to get 10rds into a 12rd mag. I took it apart and discovered what others here have already said; there is no way 12rds are going to fit into a 12rd magazine. If you take it apart and drop 10rds in and then the follower it sits flush with the very bottom of the body.
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And if you drop in 12rds and then the follower it sticks way out.
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Also the spacer in there does not lay flat and is bowed. That means when the first few rounds loaded get to the bottom of the magazine the nose is forced into the binder plate/front of it. So it'll at the very least deform the tip of the bullet ruining it's BC and make it more difficult to load that last few rounds as they scrape down and potentially push the bullet deeper into the case changing the OAL.
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