Most travelling in the day was on horse back, and the rifle was cradled across the saddle behind the horn. The constant rocking motion was hard on the lower forestock, so sometimes, a wear plate was inlet along the bottom of the forestock between the lock and the entry pipe.
In this case, since the builder feels the wood is too thin along the bottom of the forestock as a result of the ramrod hole "going low", he has elected to support the wood with a metal inlay, called a "wear plate". Here's an example: