One interesting thing about RL16 and IMR 4451 is that because of the copper removal function, your first groups you shoot may not be great .Depending on how much copper is in your bore, your groups may improve if you shoot a few more groups and the powder takes out some copper. I've seen this happen on several rifles. Also, if you shoot with some non-copper removing powder, the "copper cleaned" accuracy can go away, and will need a few groups to return.
I acknowledge that bore cleaning might do as well.
Your mileage may vary....
