I have just started casting using a lee mold for 500 grain .459 bullets for my custom built High wall, the barrel is a Green Mountain with a bore of (this was checked for accuracy) .458 across the grooves. I decided to buy a Lee sizing die and lube kit but all they have is a .457 die, what the dickens is a .457 good for? Maybe I am missing something but would .457 be too small for a .458 bore? The few bullets I have cast so far appear to be .459 but they are not perfectly round, being out-of-round by nearly .001, and so I thought a sizing die and lube kit would produce lubed bullets and at the same time correct the slightly out-of-round problem. I tried .458 cast bullets from Midway in my 45/70 Marlin but accuracy was poor so a friend suggested I try a .459 which turned out to be far better even though it was the same weight. Thinking the same may be true for the Green Mountain barrel since it slugs almost identical to the Marlin I just fail to see the use for a .457 slug. Why size down to .457 am I missing something?