This would be news to German gunmakers who routinely sight in their products using a Preuss device, which has many of the same features of the Lead Sled. I don't hold myself out as an authority on double rifles, but I have personally witnessed the regulation process at the Krieghoff factory, and I know that the rifles are not regulated unsupported.

I have never used a Lead Sled, only my home made device, which operates on the same principle, but there is all kinds of give when the recoil takes place. The whole device recoils an inch or so, but with far less velocity or energy than that of the unsupported rifle.

I have used it with a rifle developing 26 fps recoil velocity and 100 ft/lbs of recoil energy with no ill effects either to the rifle or to myself. If the stock breaks, it must not have been held firmly against the rear support.

When I was taking high school physics, the teacher demonstrated inertia by dropping an iron plate to the floor with an egg resting on top of it. The egg broke, of course. However, if he taped the egg firmly to the plate, the egg survived the drop unbroken.

I always support the foreend with my hand and rest my hand on the front bag. This seems to preserve the normal point of impact and at the same time prevents the muzzle from rising unduly.