I dug back into my old reload records for that rifle and I found that I had not shot anything bigger than 55 grains in this barrel. But, in the previous barrel (same twist) I shot the 63 gr Sierra flat base extremely well and also the old 60 grain Nosler Solid Base Boattail. This afternoon I shot my most recent reloads with the 60 gr Partition and they were in a vertical pattern. Just to be absolutely sure that the problem wasn't me, I shot 3 55 grain Ballistic tips into about 1/2 an inch and precisely 1 inch above aim point. So it isn't me, and the gun isn't busted. It's that bullet and load. Tomorrow I try the Reloader 17. I want to shoot that darn bullet at the pigs. I have a lot of that bullet and a lot of pigs and time is wasting.
I do also have a bunch of the 63 gr Sierras and the 65 gr Sierra GK. If I have to give up on the Partition, I'll see if I can stabilize the 65 gr Gameking. That bullet shoots great in my 223. If all that fails, I'll try to get some of those Winchester 64 grainers - which probably won't be easy.