5.56X45mm
Milforum Mac Daddy
My only deal with a bull-pup is you can't shoot it from your weak side (left side). The extrator is next to your ear. So the shells hit you. With the AR-15 you can shoot from either side. The extrator is in front of you and there is also a shell deflector to prevent it from hitting you. The only Weapon that I like other than that is the FN P90 or the old Calico SMG. They ejected the spent cartridges through the bottom.