Modified version of the Belgian FN combat rifle - bore 7.62mm and extremely heavy to cary in the field. Later replaced by the R4 and R5 versions of 5.54mm bore. The R1 is now a museum piece. It was onerous to clean in the field, but could stand more dirt and nonsense than the M16A
You don't clean your R1, bro, you're not gonna be able to shoot that terr!!!