I'm probably the one you read about having not good luck with 3fg 777 and powerbelts.

I do like the 3fg cut with heavier saboted bullets and I'm gonna try it with some heavy conicals too. But when I used it with PowerBelts, the little cups did not want to release from the bullets and that really threw the accuracy off. And I always loosen those cups and put a little bore butter on them before shooting them too - my only explanation is that the 3fg makes a little too much pressure and it affects the cups ability to fall off.

For the record the loads I used were:
348gr PB with 90gr of 3fg 777
405gr PB with 100gr of 3fg 777
444gr PB with 100gr of 3fg 777