they were all pretty slow back then.
i think my 223 from the early 90's is a 1-12 it certainly has a 55gr cut-off and does 5 times better with 50-52's.
i've tried 60-64's in it and the groups were round, just a lot bigger.
it does fine with cast bullets in the 60gr range even at medium speeds though... surprisingly about as good as 55gr. jacketed.