If you're loading for a rifle with Enfield rifling (unaltered Number 4, old Number 1 Mark III*, P-'14, a few Rosses) just remember that Enfield rifling really doesn't like boat-tailed bullets all that well.
I get my best results, insofar as accuracy is concerned, with 37 to 38 grains of IMR-4895 under a Sierra 180 flatbase bullet, seated to OAL length of a Mark VII Ball round. This crowds the rifling a bit, which is needed because of the different ogvie shape of the Sierra. This puts out about 2250 ft/sec from an SMLE, which is the by-test most accurate speed for the Lee rifle with the 25.2-inch barrel. With this, I get half-inch out of a Lithgow SMLE, 1 inch out of an unaltered as-issued NRF and half an inch from a 1910 Ross.
For a faster bullet, try the Hornady flatbase 150, seated out so the whole cannelure shows. Very zippy and quite accurate.
Whatever you do, be sure to have fun.