Unfortunately, changing to an STI grip module does not allow the gun to accept STI magazines as the metal frame of the gun also has to be permanently modified for that. Since extra factory Bul magazines were still unavailable when I purchased the gun, I'm using modified Remington 1911 R1 double stack magazines (same basic magazine tube as the Bul magazines) with Arredondo Plus-2 extended base pads for Para/Remington magazines (also modified to fit the STI grip module with a tactical magwell) for a 20-round capacity. To get the magazines to work in the gun I had to increase the height of the magazine catch slot from 0.150" to 0.230" using a Dremel cut-off wheel and a small square file, and shave off just a small bit of material from the very top of the magazine to ensure that it doesn't drag on the underside of the slide. I also had to tune the feed lips of each magazine to get the gun to feed reliably, but this inadvertently resulted in the slide locking back with one round still in the magazine. I tried trimming down the followers to resolve that issue, but I believe the enlarged mag catch slot introduced too much deviation to be 100% reliable, so I just modified the followers so that they don't lock the slide back at all. Since the gun's intended usage is USPSA and 3-Gun where you rarely run the gun dry, I'd rather the magazine not lock the slide back when empty than have it lock back unexpectedly. If I absolutely need the slide to lock back on an empty magazine for a specific stage or scenario, then I'll use the factory Bul magazines.