First an itching question I have, what is the difference between 5.56x39 and .223 and 7.62x39 and .308?

That being said, I want an AK. I would prefer an AK74 in 5.45 or .223 but would take an ak47 in 7.62. Money is the deciding factor now and will decide this issue for me. I have been looking around and the prices for this ammo doesnt seem to be that different, or typical for that matter. They vary in price greatly.

I want 5.45 but if its not significantly cheaper than .223 than I would just get .223 because it is domestically produced in the usa. I see 1080 5.45 rounds as mil surp but i think they are corrosive. New rounds seem to be on par with .223.

What is the true deal here? 5.45 is no where near as plentiful as .223 online. Looking at ammunitiontogo.com