Hey Jacko - your 'first' results are better than a lot of guys get - previous experience shows.

Is this rifle a rolling block?

Instead of "HAVING" to use a gas-check mould, you can usually use a card wad instead, for bullet base protection. A buffer, like GREX or Puflon also works. Just make sure the wad is under the bullet, not a distance below it on the powder. The 'filler's prevent a space between powder and bullet/wad. Since your mould is casting .459" - they are perfect & should be shot, as-cast - no sizing and with a card wad and that WW alloy, you should have no leading to 2,000fps - IF the lube is a decent one.

In a single shot rifle, bullet tension in the case is almost immaterial, so you can adjust the sizer die up, to only lightly size the case mouth for easier bullet fit - but do what shots best.

With straight smokeless powder, I'd be inclined to use a simple NRA formula lube, like 50% alox, 50% beeswax- ie: RCBS, Lyman, and many other compercial wax/based bullet lubes.

If you want to mix your own with good beeswax, try 60% beeswax/40% Vaseline. It worked wonderfully for me with both real black powder and with smokeless powder all the way to 2,200fps with .45 and .50 cal. bullets.

Failure of the lube/ie: leading :

1/. leading just ahead of the chamber means the lube is too hard, normally. Failure of the lube, ie: 2/. leading at the muzzle usually means not enough lube and 3/. leading one end to the other means poor lube. There is a crossover between #2 and #3.