Can I shoot 5.56 & .308 Nato in .223 & .308 Win Savage rifles?

I wondered with some surplus .308 NATO ammo for sale out there if it is safe. I have also seen a lot of 5.56 ammo available.

My gut says probably not, but I thougth I would ask.

you can shoot 308 nato in 308win chambers but be careful shooting 308win in the Nato chamber. Nato chamber is longer.
you are not supposed to shoot 5.56Nato in 223rem chambers but you can shoot 223 in 5.56 chambers.
Nato chambers have a different throat configuration than .223rem. 5.56Nato is good for 60000cup where the 223 is good for only 50000cup

The .308 NATO should be no problem but be careful shooting Win in the NATO. The 5.56 can be. There is no definite answer on this one, it just depends on your gun. If you have a 1:12 or 1:14 twist .223 you may have some pressure issues. If you have a faster twist then the throat should be cut long enough for it not to be a problem. I have one rifle that will shoot either or easily but my .223 Encore and my buddies rifle will not. We end up with popped primers in those.

I have a 308, and I will not shoot 7.62 NATO. When I chamber a round, the bolt is very hard to close. I have about 1000 rounds of surplus South African ammo. The stuff chambers fine in surplus rifles. The only way to find out is pick up a few and try it. YMMV.

The chamber pressures for the .308/7.62 NATO and .223/5.56 NATO have the same chamber pressure rating, there are two things that confuse some people. The older method of measuring chamber pressure was CUP (copper units pressure) where a copper crusher pellet was used, the new method of measuring chamber pressure is with an electronic transducer and the pressure is written in PSI. The pressure readings using both methods would be approximately 50,000 cup and 60,000 psi for the same pressure reading. A simple way to look at it would be like 60 mph = 100 kph, both are the same speed just measured differently.

The second difference is NATO chamber pressure is measured at the neck of the cartridge case and commercial American SAAMI pressures are measured at mid cartridge case. NATO EPVAP testing methods standards read higher than commercial pressure reading leading to even add more confusion.

The only real difference between the two cartridges is the M16/A4 is now throated for longer bullets and .223 rifles with 1 in 12 or 1 in 14 twist rates will have pressure spikes if the 5.56 with its longer bullets are used. NOTE: The European CIP the equivalent of the American SAAMI considers the .308/7.62 NATO and the .223/5.56 NATO as having the same rated chamber pressures.

Cartridge pressure standards
http://kwk.us/pressures.html

5.56mm NATO versus 223 Remington Chamber Differences
http://www.m4carbine.net/showthread.php?t=55149

Thanks for the info. What is the twist rate on the Savage 111's in 308? Is there an ideal bullet weight for the twist?