It seems that even if I wanted to do the full USC/UMP conversion, it would be impossible since there is no way to get 45 cal 25 rnd mags. The only site that seems to sell stuff related to the conversion process is HKparts.net. Is converting an USC to a USC/UMP even do able today? My current plan is just to SBR it, but I will still have to deal with 922r. The more I think of it, the more it seems logical to go all the way with the conversion to get 25 round capacity rather then wasting 200 bucks on a lower reciever that is registered to hold 10 rnds.