OK i admit my full auto experience is limited to renting a MAC 10 at a gun range and shooting a USMC M16a2 on a tigerr cruise years ago.. i must offer these two opinions...
Man maybe I watched too Much Combat with Vic Morrow and Rick Jason.. but Cpl. Kirby's BAR sounded WAY cool. Ane the idea of shooting a full auto 30-06 at 400-500 yards with 172 grain MG bullets or 150 grain tracers just makes me drool. Last gun show I saw 3 BAR full autos ranging in price from 18000-25000 dollars depeding on manufacture. (They even had a colt NAVY model)
As far as modern guns go... the dimunutive Bizon SMG from Izmash. a 9mm Makarov smg with a 66 round helical magazine in a shortned AK based reciever.. tasty. (would probably deafen you with that ak74 style muzzlebreak)
But it looks cool.
Ahhhh well maybe someday...