If you’re looking for a 5.56 rifle but don’t want an AR-15, your next best choice would arguably be the Ruger Mini-14. The Mini-14 is essentially an M1A that has been scaled down to fire the 5.56 round, and therefore has an essentially identical manual of arms. Ruger makes numerous versions of the Mini-14 today, including some that can fire either the 5.56 or the .223, others that can just fire the .223, others that fire the 7.62x39mm, some with a wood stock or synthetic stock or folding stock, some with a flash hider and others without it, and so on.
Ruger Mini-14 (7/14)
Submitted to "The Best Semi-Automatic Rifles of all Time"