Make sure your have the new mags, with 1 or 2 on the back to the right of the glock symbol. Those have the correct spring/follower combo, and I think they tweeked the feed angle. I had the problems. It mostly happens during awkward shooting grips like one handed, on the ground, or close quarter collasped grip. Basically, I think the gun just becomes more sensitive with the light on it, but its never consistent. I've tried to make it malfunction by having the limpest hold on the gun possible. And it runs 100%. Next SWAT training, I'll be going through a course and I'll have two malfunctions, its wierd
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Best advise, get the light, the gun, and a lot of ammo. Shoot it from every conceivable awkward position, chances are if it runs 100%, then you will have no issue. Also keep up on maintanence schedules, on the recoil and mag springs.
Thats my $0.02.
Edited- Also Safariland 6360 is the shit, the best holster I've had yet. Very fast and secure.