Your underfolder is a old Federal Ordnance unit. Got one on my truck gun; barrel chopped to 16.25", Millett peep sight, great compact unit. Granted, it's a "minute of pie plate" gun, but for a truck beater it does just fine. As far as mags go, check out Thermold mags. I've been using them for years in my Mini, never had a single malfunction.