It's a video about a real steel gun by Larry Vickers in this Vickers Tactical video and this episode covers the M3 Grease Gun. This was put into service by the U.S. Army a year after the Japanese attack on Pearl Harbour in World War II, it uses the .45 ACP round that is used by the Thompson SMG but is lighter and cheaper to produce, but less accurate. A version for airsoft is produced by ICS Airsoft.