OK! I did a little experiment! I got out my .303 and braved the cold weather, (it's 50 here) and fed some .25-35 ammo through it. It fed nicely and extracted and ejected, so the difference in rim diameter makes no difference, as far as I can tell. So, if the .25-35 barrel fits and headspaces properly, sounds like you have a switch barrel 1899! I would have a gunsmith check the headspace, just to make sure. Uses same gauge as .30-30.

Graf also has some .25-35 ammo. http://www.grafs.com/retail/catalog/...eywords=.25-35