The Lee dies were built to specs researced by someone on one of the Martini boards; they were made to size cases to fit just about any nominally correct .577/.450 sporter or military chamber there is (Victorian era "standardisation" and manufacturing tolerances, you see), so they tend to size way down for most rifles.
Brass sized from brass shotshells (known as balloon head) has a different construction to solid drawn; there is more capacity in it, and is warned against use in rifles with loose headspace due to the possibility of rupture. There used to be a sticky post about the phenomenon on the Gunboards MH board; not sure if it's there still. I can't comment - I always use Bertram solid drawn 2nds.
I'd say a solid copper slug of .465" is too big. The nominal ususal bore diameter is .450, with groove depths out around .465". Not really sure though about non-tox bullets in such a rifle. There is a fan club of internet MH people who advocate relatively large diameter bullets in them to account for the taper bore. I'm not one; the bullet should upset and bump up to fill the rifling on firing.
Re: Recoil - from standing, kneeling or prone? I find standing and kneeling no problem with 90gr 1P and .462" 500gr gg. I'm flinching badly after a couple of rounds prone though!
What are you using?: Mk I-III, Mk IV, or something else?
RG
