Well, crimping should not be necessary on a bolt-action mid-caliber rifle.
It is best used on tubular magazine lever-actions, semi-autos, and very hard kicking dangerous game calibers.
It will possibly shorten the life of your brass because the crimp works the brass more.
As for neck sizing .303 in 7.62x54R die, I don't know.
Chamber specs show the 7.62x54 case neck O.D. to be .336".
The .303 British is shown as .338".
Also, some die sets for either caliber come with expander buttons for both .308" & .311" bullets.
I guess some experimenting & measuring would be in order.
rc