Even on snow, would it really slide that much? Would the horizontal component of the force overcome the inertial moment of a mortar large enough to need a sled that size?
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Don, I believe the sled's main function is to move the gun through the wilderness in the snow not as a recoil mechanism. Even then looking at the photo, I think it would be a major chore in deep snow. Probably a major chore no matter how much snow for that matter.