There are a few choices. But I think the preferred is Badger Ridge. Type Remington 700 ml conversion on your computer and the Badger Ridge conversion will be there. It allows the gun to shoot BH209 powder with a 209 cap. The conversion is made so the 209 primer will not leak around the primer. You may or may not know you need to have a sealed chamber to shoot BH209 powder. It needs to be in a confined space and a #11 or musket cap will not do that. They leak around the cap. Thus the chamber is not sealed. The guy from Badger Ridge lurks here. Maybe he will add a comment.
Others may have a different conversion preference. I have not done it so Im just going by what I read.