My neighbor of only couple houses away had such a gun, and we would shoot it at a farm location available to me whenever and glad he was feeding the thing. He had built a square steel tube that fit in his trailer hitch, come out a foot or so, then straight up and back a bit with an old butt shaped tractor seat on it and the gun mtd. just in front of you.
It literally shook the truck when we set it on full auto to shoot at the big boulder some 1000yds. away painted white so we could see the bullet strikes. Only thing he would ask of me was to let him use the property for shooting it and to help him reload during the week so we would be ready to go for the weekend. He ended up buying a press from some outfit in California to reload and that press was something near 4' tall but that is one big boy cartridge. He had several machine guns, all legal, but the "ma duce" was definitely his favorite. He passed away few years ago but we had some times together in those days, miss him.