It’s a perfect fit. Just follow Chris’s video except for the lifter spring. The m60 spring will not work with the m99 feed ramp block, so you need to use your origingal spring. I went with the m60 feed ramp block upgrade from Brownells. Ran 50 mini mags through it as fast as I could pull the trigger with no issues, runs great. No more feed or extract issues. There are a few tweeks and tricks involved in the feed ramp block upgrade. Happy to share what made mine work.