Good to see you found the problem. Another thing to keep in mind is that even with a correctly bedded rifle, sometimes what you experienced can occur, and it often can be solved by changing the distance of the bullet to the lands. Some guns like a fairly long jump, say 0.020" or so, and some may want to shoot best just "kissing" the lands or on them. I have also had "two-grouping" correct itself with either an increase or decrease in the powder charge. In any instance, watch closely for pressure signs and adjust accordingly..