Raimey,
There is no way I can say, with certainty, why the pictured gun had one bushed striker and one unbushed.There may be a couple possibilities, but absent a complete history of the gun, you will have to choose the one you like. It's possible that the original striker was improperly located, requiring recocating. It's possible it was bushed to correct some defect in the casting/forgeing from which the action was made ( the double rifle that was stolen from me had a small defect that only caused a peculiar mark on the primer;which will identify it if I see a fired cartridge).It's possible that an extra set of barrels was made for it, chambered for a higher pressure cartridge, which is now lost.
I don't know if there was one reason for bushing the strikers.My Meffert drilling,with Dural receiver, had bushed strikers for all barrels (prewar).I watched Walter make double rifles and combo guns chambered for 7x65R and 30-06 w/o bushings.Some of these had o/u shotgun barrels.If the gun was not made with "hounds tooth" strikers,replacing strikers with bushings isn't especially easier than those without.It's not the bushing itself that's important, it's the diameter and fit of the striker.Certainly,nitro powder and solid projectiles, can cause conditions requiring bushed strikers to address them,sometimes;but it's not the bushing,it's the diameter and fit of the striker.On the other side of the equation, a rifle size striker will fire shotshells, just fine.
Maybe we can talk more at the gunshow Sat.
Mike
