I concur with rockrat. It looks like you're trying to get around 2500 fps velocity with the #311466, but that charge of Win 760 might only be getting you around 35,000 psi. You could be getting inconsistent ignition and/or burn with that powder. The first thing that I'd recommend is switching to magnum primers.

I've had very good results lubing powder coated bullets. I only powder coat the driving bands on bore riding bullets, and don't coat the nose. I use copper gas checks, and swirl lube the bullets with 45-45-10. Prior to loading the bullets I rub the base of the bullet against a rag to remove any lube from the bottom of the gas check. This prevents any of the gun powder from sticking to lube on the bullet base, and possibly interacting with it if the ammo gets hot from being in the sun or hot weather. Yesterday I was cleaning up some stuff out in the garage and came across some targets that I'd forgotten about. Three different targets had sub 1 inch groups on them shot with cast bullets, so yes; PC combined with lube does work! (disclaimer: those targets were shot with weight sorted bullets & neck sized brass, on clear, windless days where the stars aligned and I got extra lucky)