Replacing that awful BSA breech pin with a bolt?

[TonyL]

But shims will reduce the length of the breech/fork contact area. on a well fit meteor/Supersport, the breech block contacts the forks all along its length.

Plus, on a BSA, the pin is out of center of the barrel block. The barrel is brazed or sweated on, so the breech block does not have the height to provide full contact area for the shim.. so almost half the shim will not have contact with the breech block.

Understood. And highlighting even more shortcomings with the arrangement. The more you think about it, BSA's arrangement was far removed from the ideal.

Even those Wobblies had a fuller, more substantial, proper breech block.