I always thought bayonet lugs to be silly on civilian AR's.. I am never going to attach a grenade launcher nor am I looking to stab anyone with my rifle. Dremmel plus Rustoleum high temperature grill paint. Also the reason I had no problem getting rid of my M4 type barrel before I came to NJ. That recessed area on the barrel is to fit the M203 grenade launcher. Just a thinner barrel to heat up quicker IMO..