As well as the barrels fitting the the crosspin properly to hold the them on the face,when the gun was new it would have had a bearing between the front of the back lump and the action.This is known as the draw.On the more expensive double rifles,and now on the shotguns the draw surface is detachable,thus being replaceable.It is important,especially on the larger caliber rifles that the draw has a good bearing,otherwise the action will tend to stretch resulting in the gun coming off the face.