Tuning 45 ACP mags for 40 S&W

[pointerman1967]

I am going to use my Wilson 10 round 45 ACP magazines in my STI Trojan in .40. They work very well, but after cycling through the magazines at the range this weekend a couple of them were popping the top round as I inserted the mag. Any guidance on what gaps I should tune the feed lips to in order to make the .40 feed more reliably? Would love to keep them close to 45 spec so I could continue to use them in my 45 as well, but since I only plan to use my 45 as a backup in case of .40 issues I would rather ensure the 40 cycles 100%.

[MikeRush]

My double stack 40s are set to .380 in the back and .385 in front, I think you want it to present the round as high as you can without it popping out.

Edited November 4, 2014 by MikeRush

[Aircooled6racer]

Hello: I use 0.394" front to back for my 40 mags. They also work in my 45 as well. I only use 45 mags in my 40 single stacks. Thanks, Eric

[bountyhunter]

Be careful on round height. If the feed lips are too wide, the slide will lock back with one round in the mag because the follower gets high enough to hit the slide lock. I always try to get it so the round is high enough to feed well but not higher than that.

If it's any help: when I "adjusted" .40 mags to use 9mm, I found that narrowing the feed lip spacing by 1 mm (about .040") worked very well. However, not all mags have the same spacing so you want to tweak for best fit.

[pointerman1967]

To clarify, I am talking about single stack magazines here. Not sure if that makes a difference, but thought I would clarify.