You'll have to check this yourself. It's probably stamped in the side of the barrel of the rifle, near the receiver. Yes, it's probably 308 Winchester, but there are lots of others that are incompatible.
If he has something besides 308, or it's a different 308 cartridge (and there are a couple), they won't be compatible, so you won't find out from people who can't look at the rifle.
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