As others have said, slug the bore. MNs (and British Enfield) bores can vary several thousands from the nominal bore diameter.
Select a mould that is right on bore diameter to about .001 oversize. If youi get one a bit more than that, you can resize it - Lee sells a very cheap but effective sizer for about $12.00. I also like Lee moulds and have quite a few of them - Midwest (
www.midwestusa.com) sells them for around $19.00.
For rifles, you want a fairly hard alloy -- or keep the velocity way down. The best thing is to 'ask the rifle' -- cast and load what you've got and see if it shoots well, or leads the barrel. If you get leading, clean the barrel and harden the next batch by adding other metal.
For this rifle, I'd suggest Ed Harris' "The Load" -- 13 grains of Red Dot behind a 180 grain bullet.
Most moulds for rifle bullets are gas-check moulds. A gas-check is a little copper "saucer" that fits on the base of the bullet and protects it. Hornady makes gas-checks you can put on by hand. Other makes are crimped on in the sizing process -- an unnecessary step if you have a bullet that doesn't need sizing.
I like to lube with Liquid Alox (also avaliable from Midway.) You don't need a heater or sizer-lubricator for it, and it works very well. I float the Alox bottle in hot water to liquify it, dump a handfull or two of bullets into a plastic container, squirt in a little Alox, and shake until golden brown. Spread them on a sheet of waxed paper and allow to try for 24 hours before loading.