Look like a 1903 A-4 that's been modded up a bit. Originally a ww1 rifle but used in ww2 as well including as a sniper rifle.
There was an A3 too.
If the barrel and receiver has few if any markings, then it was probably made by Smith Corona (the typewriter company) as part of war.
If it has a cutout on the left side, it was made to be able to use 30 cal pistol ammo. Look up Pederson Device.
[This message has been edited by maryjane (edited 01-11-2021).]