I have the military style 22 kit for my AR, I think it is called the M261, uses an insert in a normal 20rd mag, and works very well,
I usually get a 1-1/2 to 2" group at 50 with it in a 1/9twist barrel using standard velocity ammo (PMC target or Rem green box, NOT subsonic)
I haven't had any luck with consistancy with Rem subsonic
drawback is no bolt hold open,
I've been considering a dedicated 22 upper from either compass lake or accuracy speaks,
just haven't had the extra $$'s to order,
HTH, YMMV etc