Mike,
It also might be a bad batch of bullets--though if that particular lot has shot well in other rifles that's unlikely.
One thing I learned when fooling with a Juenke machine for a couple of years is that not only do bullets vary in "balance" from lot to lot, but can be damaged enough in shipping to result in decidedly mixed accuracy.
Though the problem certainly can be a specific bullet not matching well with a rifle's chamber/throat/barrel. Which is why when I find a certain bullet not responding to trying different variables (powder, seating depth, and even primer) I tend to move on. There are too many good bullets these days to keep trying and getting the same results. Though I do tend to have more different bullets on hand than most handloaders--generally at least a dozen and often twice that many in any caliber.
