Back before swamped barrels were commonly available, it was somewhat common to attach a shim to either the side of a straight barrel or to the bolster of lock to get to a wider wrist and proper stock architecture for earlier styles. Sometimes the shim was tapered wide at rear to narrower at front, to get the flare and wrist and breech shape that a swamped barrel would provide. Sometimes a shim would also be added to the frizzen base. This is why certain lockmakers still put a too wide bolster on their locks. Bob
