Can the lead sled be an issue? NO idea what they are, short of a recoil reducer.
The sled places another variable between you and the rifle...are you THAT recoil sensitive that you need the sled? If so...recoil sensitivity may be adding to your group sizes.
Leadsleds if used properly, can remove, or atleast mitigate, the shooters influence on the shot. While i dislike them for sighting in, i think they provide a good platform for testing rifle accuracy.
As to recoil sensitivity, again the 06 is on the edge of what the average shooter can tolerate with little or no practice. 50-100 rounds in a short span and even experienced shooters will begin to get fatigued. So he sleds not a bad idea for load testing.