TOP GUIDELINES OF WHAT IS A HK416

This can be mine, all Plastic. This is certainly as I took the cover off no mods. My assumed, is there a difference between the new plastic assy vs the metal a person in how the package would function? You guys who say you've carried out 1 with no challenges, which was it plastic or metal? O-ring tensioned FH is top quality. I dilemma how effectiv