My guess is the mold is sized for pure lead, and your lead has a small amount something else in it that causes them to come out on the light side. Not surprising at all. When you have "too much" tin or other metal in the mix, the bullets come out even lighter, and oversized, which can really be a problem.

I'd say you'd never have a problem obtaining hunting accuracy with bullets that vary in the 5 gr range, but of course, the less variation the better.

That is great shooting. I've had days when I got groups like that at 50 yds. I've wondered how I'd do at 100, but since my Renegade wears a peep and my eyes aren't that great anymore, I think those limitations would contribute to more inaccuracy than the gun. It is fun when you can call shots, and know exactly where the bullet will hit when the gun goes off.