Using 45 Cal Mags For 40s&w

[Tester]

Hi,

I am shooting a 1911 in 40S&W, in USPSA Limited-10 Div. that I built from parts. The gun shoots great but has a habit of locking the slide open with one round left in the mag every now an then, but usually at the worst time in the COF. I am using Chip McCormick 45 ACP 10 round Power mags because I have them when I shoot 45 ACP 1911 in L-10. According to the FAQ these mags can be used for 40 cal but there were some small modifications to make them work better, but they weren't listed. I have a number of 40 cal mags but they don't work when you load long. The CMC Power mags have fed very well and are reliable so far except for the slide lock problem.

I think the problem is that there seems to be slight upward contact between the lower leaf of the follower and the slide stop pad when the last 40 cal round is ready to be fed that sometimes, with some mags locks the slide open. This is due in part to the difference in diameter of the two rounds and that the 40 sits a little higher in the feed lips. I think there are two possible fixes to this early slide lock problem or a combination of the two. The first would be to shave the bottom of the slide lock pad so there is some clearance between it and the mag follower when the last 40 cal round is in the mag. This would leave the mags unmodified and usable for 45 also. The other method would be to bend the lower leaf of the follower down enough so there is clearance between it and the slide lock pad with a 40 cal round in the mag. I'm not sure if this would cause a problem when using the mags for 45 ACP or not? The other question would be if you did bend the lower leaf of the follower down how long would it last with the spring pushing it back up all the time.

If anyone has any ideas or suggestions please make them because I want this gun to work more reliably because it is so much fun to shoot USPSA with.

Thanks

Steve

Edited October 19, 2005 by Tester