Two suggestions:
Try some groups with the bullet at different seating depths. I once worked up some loads with the 130 E-Tip in the .270 Weatherby, and because of the "freebore" the bullets were simply seated out as far as they could be in the magazine. Groups were around 1-1/2", so I started seating the bullets slightly deeper for each group. Groups started shrinking until they were around 1/2" to 3/4".
But once in a while a barrel simply won't match up well with cylinder-shank monolithic bullets, and trying different powders doesn't seem to have any effect. E-Tips have shot well in maybe 85% of the rifles I've tried them in, but once in a while they just don't.
