OP,
IF you are using the OEM 700 S/A mag box w/ the 221/222/223 follower w/rear partition piece installed you will need to cut a single round "sled's" length to fit.
If the partition piece is not going to be used whittle a piece of 1/2" thick aluminum w/ a milled radius and an inclined slope for proper feeding as guntech stated.
The radius cut in the "sled" has to provide clearance for the bolt body to slide fwd/aft w/o binding.