can't speak for an AR, as I am a bolt guy....

but around 10 grains in a bolt gun will work with RL 7

seems like a 221 Fireball would be a better choice if ya were doing a new barrel


"Minus the killings, Washington has one of the lowest crime rates in the Country" Marion Barry, Mayor of Wash DC

“Owning guns is not a right. If it were a right, it would be in the Constitution.” ~Alexandria Ocasio Cortez