Hi, new member. I own a mdl 1917 Army. The gun is missing the butt swivel which I have just ordered. The question I have is in regard to the butt swivel hole, it is filled with a gray matter which appears to be lead. Could this have been done at the factory, or is this just something a prior owner did? Ser# 95xxx. If this plug was factory installed I would hesitate to remove it. Any info appreciated.