Here are the specs for checking headspace on the RFI 2A/2A1 in caliber 7.62.
1.633 GO
1.642 NO GO
Do not fire these rifles with anything other that 7.62 NATO ball or an equivalent as Bindi says. I'll always consider these "Barney Fife" rifles. "Here's your rifle Barn", "Here's your bullet". "please put it in your pocket! Seriously, if you want a Lee Enfield as your favorite go-to 7.62, buy a No.4 conversion. They are much stronger but remember that you're still stressing the body to the limit of it's design.