For what it's worth, I took the Ruger out again and shot some Hornady Frontier .223 (with some other ammo) without issue. Don't know why I had a few misfires before. The best groups from the RAR were handloaded 62 gr Hornady BTHP over 335. Unfortunately the load is a little light and didn't reliably lock the bolt back on my 18" rifle gas AR.