The adaptors arrived (kudos to Madmax, Stefan, and ASC Armoury), and I got to fire them.
Loud, high-powered, full auto's really, really fun. There's some recoil, and the gun seems quite accurate.
Haven't done any more then random plinking yet, I'll put some .22 targets up later.
The HiCapa 3.8 is nice, but right now, I'm rooting for the M190.