Positive it's a 25-35, 25 caliber:
The
.25-35 Winchester Center Fire (6.6x51mmR) was introduced in 1895 by
Winchester for the
Winchester Model 1894. Together with the
.30-30 Winchester, it was one of the earliest smokeless cartridges designed in North America for a sporting rifle.
[2] Savage adopted it for its
Savage Model 99 lever-action rifles. The case was based on the
.30-30 cartridge.
I've also got a WWI 30-40 Kraig, still has the original brass and leather, only missing the bayonet. The original "doughboys" got 30-40's left over from the spanish american war, later they were equipped with 30-06's. It belonged to my wifes grandfather. It has shrapnel in the stock, he was carrying it in a field in France when the guy next to him stepped on a landmine. He was in France in a hospital until 1922, he was 16 at the time. He was riddled with shrapnel, told he never see 21, died when he was 80!