The FAMAS is a variation on the HK system, I believe it uses a lever rather than rollers.
Still highly reliable (with good mags). Friend of mine is a now retired Legionairre with a combat tour in Afghanistan using one. He still prefers the M4, but his FAMAS didn't let him down the times it came to small-arms work.
A straight blowback 5.56mm would end up needing both hands, a foot and three friends to cycle the action. Something like a shoulder fired Schwarzlose......
Even for 9mm SMGs blowback can be a bit much, there's some heavy bolt SMGs out there.
"And Shepherds we shall be. For thee, my Lord for thee. Power hath descended forth from thy hand, that our feet may swiftly carry out thy command. So we shall flow a river forth to thee and teeming with souls shall it ever be. In nomine Patris, et fili, et Spiritus Sancti. Amen."