difference between the stripped lower receivers?

[Maksim 1,504]

So here is a question...

 

what the heck is the big difference between all of the receivers? i figured one stripped receiver is the same as another... a shaped hunked piece of metal.

 

so so far I know steel/alloy, coated, uncoated... what else.?

[UHF 0]

The blanket answer is.......Quality. Quality of material, milling, finish. Be prepared to spend copious amounts of time at AR15.com.