As a base lets say you want to manufacture domestic AKs however you want unique options like various lengths of barrel and calibre.  Lets say standard length 16+', RPK 20' and, SBR lengths of barrel in the following calibres:

5.56
5.45
7.62x39
7.62x51
7.62x54R
12guage

Ok firstly the key component of any gun the barrel?  
Machines to make, and costs of?  
I kind of assume most of these weapons can be made on 3 types of recievers and domesticly available parts?


Pick it apart, shoot it down, or just educate me?  
Why has it yet to be done?

to many cheap import options.  when the cheap imports dry up the US companies will take up the demand.  if you look at replacement barrel made in the US for other firearms they run on average from $200-$300.  the common AK barrels that are imported are usual around $100 or less.  once the average import price gets close to thatit will be profitable for US companies to ramp up production.  any reputable barrel maker can make the barrels to what ever specs you want.  some can even chrome line them.  E.R. Shaw comes to mind.  

?