I feel your pain - that happened to me with M70 30-06 - damn thing shot anything under a 1/2-inch - the good stuff closer to a 1/4-inch. Donors don't get shot anymore at my place.
If you have a .30/06 and a pound of H 4350, just load a bunch of different weight bullets and there will be a few surprises in there. Mine loves 150gn Partitions, 168gn TTSX's and 180gn Hornady BTSP's. It likes 175gn LRX's and 200gn Partitions.
When new, it shot a bunch of sub .7MOA groups using several 150gn CnC bullets.