I bought up all of them 20 rnd and 32 rnd UZI mags 6 years ago. Had my first UZI but, what was this AR15 thing all about? Got some conversion parts from RRA and assemble a first AR15 as a 9mm. Got a job several years back where I can machine anything I want after hours. So, several dozen of them UZI mags got machined into real good AR15 9mm ones. Bead blasted and parked all of them up to last.
A 9mm AR15 is such a sure hitter under 100 yards. And, what you hit gets, plastered. Without a huge blast of noise.