I also like heavy for caliber bullets, but to see the advantage there must be sufficient target density to enable the bullet to act upon it. Sometimes my bulb comes on slowly, but I get there eventually. I am very much a fan the .375/380 gr Rhino bullet. My testing showed a .92 caliber expansion combined with 32" of penetration with this bullet having an impact velocity of 2300 fps from my .375 Ultra. I sent Crazy_Davey a few to try in his H&H, and he promptly rugged a black bear with one. But the recovered bullet showed little of the potential expansion! AHH!!! (the bulb came on) there wasn't enough density in that blackie for the bullet to open up, so the heavy Rhino was actually inferior to any number of other more common and affordable .375 bullets he might have chosen. Having said that, I don't know that a 220 Partition is the worst bullet you could load in your .308, the rifle apparently tolerates them quite well, but the wonderful thing about .30 caliber rifles is that there are so many great bullets available for them that is should be easy to have a load that is suitable for the specific conditions you face. If that sounds too much like work, then simply work up a good load with 150-165 gr TSXs, and you'll be set for anything North American and much of Africa has to offer.
Another issue that might come up with a long .30 caliber bullet from a 1:12 barrel is precession. Precession is simply another term for yaw, and it occurs twice in the flight of the bullet, first when the bullet exits the muzzle and again when it impacts a denser than air target. If the bullet is spinning slow enough that stability is marginal (which is not evident from your bullet holes) it will take much longer for that bullet to recover from the precession and come back in line, chances are it never will. I have two primary .30/06 rifles in my house, one is my Brno ZG-47 with a 1:10 twist, the other is my wife's Husqvarna 1600 with a 1:12 twist. Woodleigh .308/240s perform exceptionally well in my Brno, but they have shown only marginal stability the Husky. Thus they will not penetrate as well from the Husky, because the angle of attack through the target will not be nose on, the expansion will not be flat, and the resulting penetration will not be as straight. Therefore my wife's load is made up around 180 gr TSXs while mine are the Woodleighs.