Probably built on a recovered 03A3 drill rifle receiver. I won 100 of the drill rifles in the CMPicon auction several years ago, and all of the big guys such as Sarco and Numrich called me to try to buy mine. I believe that all of the FAUX 03 A4 rifles were built on recovered drill rifle receivers. Nothing wrong with with the receivers for that purpose, but none of the companies disclosed that fact.