Yes, I guess you would need to be rolling your own ammo for the 30-40.
The 30-40 Krag-Jorgensen round is very similar to 303 British.
As for the rifle itself, they are beautiful rifles, very well machined with extremely smooth actions.
The magazine is a bit different, loading from the side instead of through the top. I think it was actually the inspiration for the .303 Lee-Enfield
The ones I saw were very accurate and they made Enfields look like trash as far as fit and finish went. They really were pretty, kind of like the .303s made by BSA.

I would agree with staying with the designated bullet calibre as a general principle, but as I mentioned Enfields are interesting.
During the war years they accepted wide tolerances on the bore diameter in favour of increased production.
The bores can be anywhere between .308 and .318.
So if you are handloading and can't find .311 or .312 bullets trying a box of .308 and seeing how it groups makes good sense.

Somebody mentioned Mark VIII (Mark 8) ammo.
If you run into Mark VIII leave it alone. It was made for Vickers machine guns and had more powder in it.
I think it stresses the action too much in a rifle and it tends to burn the barrel more too.
Besides that it will be really old surplus FMJ and you don't want it for hunting anyhow.
If you are going to shoot surplus ammo stick with Mark VII (Mark 7)

The only other thing about ammo is most of the current surplus ammo from Eastern Europe uses the Berdan type of primer which you can not reload.
That is fine if you are not reloading or if the shells are cheap enough to throw away the brass, but if you are reloading you might as well by reloadable brass if you can. That means Boxer type primers, most shells made in the west use Boxer primers.

Just some final bits of trivia, SMLE (smelly) stands for Short Magazine Lee Enfield.
Some of the early .303s were made as calvary carbines. They were shorter and had a slide to shut off the magazine.
>.303 Savage is not the same as a .303 British, even though the bullets are the same diameter.


I think I have mentioned almost everything I know about .303 in this thread now.