I got the mean arms 9mm adapter to complete my 9mm carbine build. (Technically a pistol). These run about $29 each and replace the normal follower in a gen 2/3 pmag 30 rd. I was skeptical at first based on the reviews I watched and read. I ran 250 rounds through it yesterday with not a single issue. I was using the wrong buffer and spring in my pistol brace so that got chewed up a bit, but the gun ran awesome! Would highly recommend to anyone looking to do a 9mm AR build without a dedicated lower.
Interesting, I’ll have to take a closer look at those.