An actual Armalite Model 01 would have been made between 1959 and 1961, and is both C&R designated, and usually NFA registered. The original AR-15 was a select fire design, through both models 01 and 02 before adoption by the USAF, sale to Colt Patent Firearms Mfg, and eventual type classification and adoption as the M16.

So what is it that you've got, that you're considering buying?