Very nice rifle!! Obviously a .67" group will kill coyotes very nicely, BUT.. yeah you can probably tighten them up some if you want. It would not be unusual at all for one of Mike's guns to consistently shoot .25" groups under perfect conditions with the right loads.
I like to know what my guns are capable of. That way I know any deviation from that is due to me.
Start with load development. Dan Newberry has a variation on the "ladder method" that works pretty well here: http://www.clik.to/optimalchargeweight
Do it for each bullet/powder type you want to shoot. You may very well find that the most consistently accurate load for any given bullet is not at max velocity. At that point you need to decide whether you want all the velocity you can get, or the best accuracy (my choice).
After figuring out what powder/bullet combo seems to work best, you can play with other "accuracy tweaks" like distance off the lands, concentricity, etc., etc., if you want to.
Next you need a REALLY stable shooting platform. Your bench looks pretty sweet for actual use, but for testing purposes you'll probably want to shoot off of concrete.
Then I like to use a rest that the gun will sit in, stable, ready to fire, all by itself. Remember you are testing the gun/ammo, and the only way to effectively do that is to eliminate yourself from the equation. I still let the gun recoil into my shoulder, especially with heavier recoiling guns, but with no pressure from me anywhere on the gun except the trigger (and guard). In other words, I'm basically not touching the gun and letting it "free recoil".
Aim the gun precisely before each shot, but for best results, you should be able to step away and come back later and still have it precisely aimed.
The thing that's sometimes the hardest to do, you'll want to pick a time when there is NO wind at all. You're testing the rifle/ammo, not your wind doping skills.
You'll probably come up with groups that will amaze you (take pics). Any other time you shoot (using "normal" techniques/conditions), you'll know that whatever differences in group size between the "test" groups and any others are entirely due to your skill level.
It can sometimes be a little depressing and frustrating to know a gun will consistently shoot .25" groups without you being a factor, and the best you can do using "normal" shooting technique is .75", but it can also encourage you to improve your abilities.
