LD, I have one, that's a MG-13 mag modified to fit, holds 25 rounds. Muzzle blast from the brake is horrendous , shooters at the bench next to you will give you dirty looks even if your brass doesn't put a lump on their head.
The gas system is adjustable with a special tool, TAPCO makes a cheap plastic one that works. Very important to have it set right or stuff breaks, and DO NOT shoot Turkish MilSurp in it! Too hot for it, Romanian or Yugo Milsurp works good, light ball seems to work best. Here's a good link with disassembly instructions right side of the page.