Softair Zone present the SRC SR4 Falcon SMG/M4 Adapter which allows one to use a 9mm-style magazine to an AEG that uses M4-style magazines... "We would like to introduce you to the SRC SR4 Falcon SMG / M4 Mag Adapter with which you can turn every M4 into an SMG. Bar magazines and SMG are becoming more and more fashionable.

However, instead of buying an expensive new Airsoft, we recommend the MAG adapter from SRC. This is inserted into the magazine slot like an m4 mag and then reduces the cross-section so that the SR4 bar magazines fit. These are available in both high and mid caps with 110 shots."