metal receiver question

[psion]

maybe im being daft, but will somebody help me out here, i recently posted a topic regarding my plastic M4 receiver, i have broken the 2 clips that the pin slots through on the upper receiver so there is now nothing that holds the top to the bottom.

i have been looking at replacements of late, and (given i am resonably good with building things and i have a reasonably high level of common sense) i decided upon a lovely metal jobby. i have not ordered it yet for one simple reason.

how the actual f*** does the retaining pin that keeps the top receiver attached to the bottom receiver work???????

the two little plastic lugs that have snapped off my receiver do not exist at all on the metal ones, will someone please explain this to me, i'm sorry if i sound mildly retarded, i feel mildly retarded! please dear god someone tell me.

 

[Nutster]

Usually on metal bodies, there are pins or molded lugs on the rear of the upper receiver that slot into the lower receiver, it doesn't need the TM style pieces on the bottom.