Regarding wedge-sealing. This involved deformation (expansion)...

Regarding wedge-sealing. This involved deformation (expansion) of a soft metal skirt at the base of the shell. The deformation of the skirt was triggered by the backward impulse of the propellant that was sending the shell 'in front' on its way. The deformation had the effect of creating a seal between the shell and the barrel, and consequently kept the hot propellant gases where they belonged - up front. Leakage of hot gases back along the barrel would otherwise create the unhappy prospect of all of the shells firing at once.

If you think about it though, what is the effect of all of this deformation and jamming going to have on the barrel interior lining? Even if the barrel is very hard and the skirts relatively soft, over time there will be some deformation of the interior lining of the barrel, and over time the skirts will (possibly) not deform enough to create a perfect seal against a roughened interior lining.

MST and others spoke about barrel wear being an issue a long time ago - long before the current propellant in self contained skirts concept. It is true, however, that single use barrels, or barrel inserts, would overcome the problem of barrel wear arising from wedge sealing. The question then is whether a throw away barrel solution could compete in the market with the current reloadable/stackable shell concept. Given that even a use-once throw-away barrel would have to be manufactured to a very high standard it seems to me that there'd be lot higher production cost (and smaller profit margin) in the wedge-sealed concept.

That's not to say that MST should let the wedge sealing technology go free if they can avoid it, just that it doesn't really stack up against the later solution.