The closed receiver design of the: AR, AUG, Daewoo, Sig 556, ARX100, Scar, etc makes cleaning inside difficult. Designs with an open top receiver (ala AK and FAL) are a breeze to wipe out (Pistons don't get as dirty in here).

JYD #123 The great one formerly known as Architect.

I am now a fictional British television police officer (currently a Detective Sgt) at Thames Valley Station. My governor is Detective Inspector Fred Thursday and it’s 1969.