A few observations, Mike.

Shooting dead level but that wide begs the question of what velocity did the Hornady ammo actually give? If it was way slow, then further experimentation with warmer handloads might be worthwhile. If it was 2100 to 2200 fps, the last thing you want to do is drive pressures way up trying to get rid of THAT much wide shooting.

I've gotten to the point that when I run across one this much out of regulation at normal velocity (again, we need chronograph results), I just don't waste much time screwing with 'em much anymore, because I know I'm not likely to get there within pressure limits. No vertical and only horizontal dispersion is easy to fix. It's the vertical dispersion that's a problem. If your ammo is producing standard velocity as corrected for barrel length with 300 grain, and making small individual barrel groups, you're set. Send it to J. J. Perodeau with the ammo and have it re-regulated. Last I heard he gets $600 for this service. He's re-regulated one for me and quite a number for friends with superb results. It's money well spent. You might find something through experimentation that works, but when they're that far out, it usually isn't worth the effort.