Buttstock Trapdoor on an 1899

[Model24]

A most interesting trapdoor on the buttstock of an 1899. Has anyone ever seen this?

https://www.proxibid.com/1911-Savage-Model-1899-Lever-Action-303-SAV-Rifle-with-Buttstock-Trapdoor/lotInformation/84701035

[Big Al1]

Nice old rifle. looks like a custom addition!