The hole is called a "prayer hole". A prayer or bible verve important to the owner was written on a piece of paper, rolled up and inserted into the hole.
Eric, I have saved every image of original and lots of contemporary Beck rifles since I joined this site. There are too many to post now, and lots of them are still in the Virtual Museum. If there's something special you need, pls. e-mail me sapergia@shaw.ca, and I'll send them along that-a-way.