I don't know what twist my Ruger 10/22 magnum has, but it won't stabilize a Federal 50gr.
I bet it is a 1-14". And it may be that your rifle just does not like that slug- no matter what the twist.
I had a late 1980's 77/22 .22 mag with likely the same twist that consistently shot that 50g Federal ammo into 1/2" at 50 yards. It was by far it's favorite load. Lighter bullets shot patterns in that gun.
