9mm ARs are a little bit more “tricky” than standard ARs due to them being blowback. Mine took a little tweaking with the buffer and spring to get it working right. A kit probably would be less finicky than random parts.
Yes, I’ve read about buffers and springs being an issue. Some people have used a 308 spring and say that fixes their issue, but I’m not sure it’s the same issue you had. Thanks.
Never had a desire for the AR platform, I’m with Sgt. Maj. Plumley on this one. Rather have an AK platform. Built a lot of different firearms and always ran into fitting issues when mixing parts. And you can’t put material back after it has been removed.