Gents, those of you that own one of these things can see how the "sled" {it isn't actually, it has three "legs", the rear being adjustable for elevation} can be weighted with LOTS or no additional weight.

My thoughts are, if no additional weight is added to the sled, it would probably present no troubles as it would approximate the resistance presented by the bench firing of a big strong ox of a man. However, if you had that thing stacked to the gunwales with lead shot, it might not move at all, that is, the inertia would be great and in such a position the resistance to the stock would approximate backing the butt of the gun up to a brick wall and having at it. The forces applied by the metal parts of the gun to the unmoving wooden parts would be great and, as with military rifles fired with rifle grenades, may be enough to allow setback of the metal parts into the wood, and thus cracking it.

But the thing is, these Lead Sleds have been around a while, and my assumption is they have been fired with a large number of heavy rifles, and if the problem of stock cracking was great and recurring, they would be outta biz, as I can't imagine the types of fellows who own $30,000 rifles letting a company get away with marketing a log splitter as a gun rest.

Xausa, can you post a picture of your device? Does it "give" at all against recoil?

The zero shift is of course another issue. I plan to check that in the future, so I'm not done with this thing.

Unfortunately, I don't have a heavy hitter to whack away with.

Now, if somebody would like to loan me their heavy, with enough ammo to do a proper test...say...1000 rounds or a bit more...I'd be happy to give her a try...