Wait a minute there. Those tests don't say nearly as much as some here contend. It's like comparing apples and oranges. The joint pin on the 21 is further from the breech face than any of the other guns. While I don't know the various wall thickness of the guns compared I suspect the 21 is no light weight in that department and may even be the thickest of the lot. But the most critical thing has to be the distance from joint pin to breach face. This factor will dwarf all others when assessing how much strain an action will endure before failure. Quality of steel is way down the list.
nial