The replaceable Shoe on a Parker is to compensate for bolt wear. The bolt holds the gun closed, this has nothing to do with the fit of the barrel breeches to the standing breech. well yes, admittedly if the bolt is so loose it doesn't fully close the barrels will be loose to the standing breech, but by merely pulling them down by hand if there is no wear to the hinge they will be tight.
I have an H grade Lefever parts gun. This gun was "Rode Hard & Put Away Wet" so to speak. Top lever is well left of center with just a small amount of take-up left. Amazing thing is the ball hinge screw can be completely removed & the barrels bolt up to the same position, tight to the breech with no discernible difference in the position of the top lever. This is of course accomplished by the shoulders on the Doll's Head. The ball joint can be adjusted back to its proper position without causing the shoulders of the doll's head to lose contact.
It is also noted I have in my meager collection two doubles which have absolutely no built in wear compensation. One is a pre 1900 J P Clabrough, the other a circa 1902 J P Sauer & Sons / VL&D Knockabout. Both have double underbolts & a doll's head. Bolts & notches in the under lugs are parallel on both with top levers always stopping at center. Both are still tight & on face. This has somewhat caused me to wonder if tapered compensating bolts do not cause more wear due to the friction from their wedging action than they compensate for.
