The Thompson mags fit VERY snug in the Thompson receiver. On my Mags I SLIGHTLY
(I can't emphasize this enough, SLIGHTLY) filed the guide rails on the rear, top of the
magazine. What this does is creates a slightly beveled point that allows feeding of the
mag into the guide channel easier.
Thompson mags to not normally "drop free" like AR and pistol magazines do. When locked in place,
they're rock solid.
As far as misfiring, did you wind the magazine until it makes an audible, louder, "CLICK"?
You need to wind high cap mags a long time until you get to the fully wound point and it clicks.
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