Odd insert in buttstock of 99G

This may be common knowledge but web searches have not been successful. My 1927 99G has an unusual feature-I think. The rifle does have neatly installed swivel eyes. In front of the rear eye is a neatly inserted "bullseye" insert not unlike those found on Marlin firearms. This insert is too neat to be a Bubba job.

This rife has a Lyman 30 1/2 sight. Also the rifle has a Hensoldt Zeil-Dialyt 2 3/4x scope. The Redfield base covers the receiver marks. This is the old style base with graduated opposing screws in the rear. Any information on this insert in the butt stock is appreciated. Sorry no pictures.

Without a photo it's hard to tell but the bullseye insert could have been a gunsmith install.

The insert, sling eyes and Redfield scope mount are all add ons after it left the factory.