I had shoulder surgery (rotater cuff repair) a couple of months ago, and was concerned about shooting anything with recoil. So, I borrowed a friends Lead Sled to check the zero on my deer hunting rifles, a 270WSM and a 243. I zeroed the 243 with a new load, shooting in the sled. I then shot it off sandbags a few days later, and the point ot impact was several inches off. I am guessing it shot one way in the sled, and another way out. You have to remember that the rifle is going to be held one way in that sled, and will be held another way when you are shooting it. It can and does make a difference. Some may argue with me about this, but the way a rifle is held and where the pressure is applied when shooting it, affects point of impact.