damn bunch of smart asses. simple question simple answer no. i never messed with rifles to much always owned shotguns. just started getting into long range target shooting. trying to learn more about it. should have asked bout the difference in the different sizes of 7.62 maybe i might not have been ridiculed wile trying to get info
Ok - all kidding aside, you'll find many shooting websites will give answers to a question like you posed that fall into the "smart-assed" category. It's usually not personal, and it may sting a little bit or sometimes be offensive, but it does serve a purpose. I rather suspect you won't forget the answers you got to this question. I also hope that you realize exactly how dangerous using 7.62x39 in a .308 might have been, and can understand why people might have responded the way they did. Along the same line, you will probably encounter both ".308 Winchester" and "7.62x51" as you learn more about your rifle. Although there can be slight differences in the chambers and pressure specs, it is generally safe to shoot "7.62x51" ammo in your .308 rifle.
If you are really unaware of the differences in rifle calibers as your question suggests, my best advice to you would be to get some personal instruction on the handling and use of your rifle from someone with expertise in its safe operation. The internet is probably not the best place if you're starting from scratch in long range precision rifle shooting. Even with your background in shotguns, I would still recommend that you find someone in your area to help you get started. The safety reasons should be obvious, but I think it would also help you become a better shooter in less time than it might take to learn everything the hard way by trial and error. Just my .02.
On another note, if you're having trouble finding .308 Win ammo, you might also check here:
GunBot find .308 7.62x51 ammo in stock
This is a robot search engine that scans many online ammo retailers websites to see whether their ammo supplies are "in stock". It lists ammo by caliber and gives the ammo load specs, retailer, price, etc. You can usually find something close if not exactly what you're looking for if you check the site fairly often and order some while it still says "in stock". If you have any other questions, send me a PM and I'll try to help you out (no smart-assed answers). Good luck.