Milled butt plate question

I have a smooth milled butt plate that is marked on the trap door with H5.
The H5 is not stamped but raised. Who made this butt plate and when?
Thanks,

On the inside? If so, may be an early Rock Island.

Yes, it's on the inside. What year would it have been made?
Thanks,

I can't be certain, but I believe the buttplate was made at Springfield Armory during WWI.

Hope this helps.

J.B.