Note I did not say, or even imply, the Jones design was "Weak". I simply stated its main "Strength" characteristic was in bolting the barrels down. The main force on a break action gun is Axial. While true the friction of the barrels being tightly secured to the frame can, & likely does, take some of the strain off the hinge but adds nothing to the flexing back of the standing breech. There are other systems which equal or exceed the aid to the hiunge. I highly suspect, though do not have actual figures to substantiate it, a properly fitted rear lump on a Purdey style double underbolt has gives more assist to the hinge joint than does the friction incurred in the Jones design.
It is also noted that most reputable makers of doubles intentionally do not bed the barrels to the frame, but have them stop with bearing on the standing breech & a thousandth or so clearance between the barrel & action flats.
A properly fitted Greener Crossbolt of course adds resistance to axial thrust at the "Top" of the standing breech, What better place is there than that to put it.
As I enjoy shooting muzzleloaders on occasion Speed is not my main consideration. If I had a double with a Jones underlever I would no doubt shoot it & enjoy it, but I just don't see it as having a major advantage in the strength department.
