Thinking aloud here -
1. Other than having yet another caliber for an AR conversion, what's the appeal? Every serviceman I've spoken with, even the Green Beret, loves the AR platform. I for one believe that familiarity is a large part of that, since they have to depend on it for their lives. Me, I have never fired a gun at a 2-legged critter in anger, so I don't have that "preference" built-in to my mindset.
Therefore, I want to ask, why not just the AK-74? I'm being serious, and would like to have an intellectual discussion... I'm not trying to poo-poo the thread. Why do you want one? Magazine reliability? The aforementioned "upper swap" idea for another caliber? Or....?
I have an open mind on this because I have at least three different people that used to be in the service (including that GB) who are asking me what should they buy for their next gun purchase! I have been steering them toward a 6.8 platform....
2. The surplus corrisive ammo out there seems ill-suited to the AR platform. I for one would like to see a sealed piston system like all of these "new" designs that are popping up.
3. Surplus ammo is cheap, but what about reloading. .221 Fireball ammo can be resized - maybe - to 5.45x39 if you don't mind throwing away about 20-25% of the rounds that don't resize properly and split. That's 1/4 of the brass, and that won't be cheap, thus driving up the overall cost for investment.
.223 bullets can be easily resized to 5.6mm (which is actually what 5.45x39 ammo is) in a bullet sizing die (aka bump die). CH4D makes 5.45 reloaing dies for about $80 a set.
What we need is 5.45 *BRASS* cases. That would do the trick for me.