"OK, I'm sold. I want a Saiga (Russian-made AK variant; looks like the best deal since the nickel cup of coffee. NIB for under $300).
Next question: .308 or 7.62x39? I need some help here."
This is a case of 'You get what you pay for...',
How much is your life worth? ($300 apparently...)
Doesn't matter what chambering you get it in, it still has a crap Russian production barrel, so it's not going to be accurate.
"...be accurate enough to hit a man out to 4-500 meters"...
NO PRODUCTION AK has ever been able to hit a torso size target consistently at 500 meters.
It was actually built to engage at ranges between 75 and 150 yards.
(and at 150 yards, things are a little shaky!)
.308 will give you a little more knock down power at closer ranges, but you are still going to miss everything beoynd 250 yards anyway, so the energy at the target doesn't matter since you won't deliver TO the target at 500 meters.
If you had gone with a M1A or AR-10 in .308 you could have had extremely accurate semi-auto that would be a tack driver at 500 meters...
Cart before the horse thinking...
If you want to shoot out to 500 meters,
Then start with the short list of semi-auto rifles that will be ACCURATE at 500 meters!
And work the list down from there...
I don't think anyone with any experience with SEGA would put it on a 300 meter list, and it doesn't have a chance at 500 meters.
Match grade AR-10, NM grade M-14, ect.
You won't get any of these for $300 either...
Start about $1,000 for a reasonable used and go up to about $4,500 from there.
Personally, I like my AR-10's in .308 and my new one in .300 WSM really kicks butt!
"All ammo is going up but with no more 308 surplus on the world market due to UN Ban on sale, 308 is around $ 450-550 per thousand."
Surplus doesn't do 3" groups at 500 yards anyway...
Surplus is lucky to do 18" at 500 yards.
Volume or accuracy, it's hard to have both!