May I suggest an alternative way of mounting a bayonet on T81. Instead of reworking the bayonet itself, knock out the pin from the grenade launcher and move it 1/4 inch forward. You ll have to drill a new pin hole in the barrel, but that's it. While the grenade launcher attachment is off, you can drill some holes in the groves of the front part- (a la Yugo SKS 56 grenade launcher) effectively turning it into a muzzle break. 