PB has a good reputation for this use. Being a medium burn rate, it generally, in selected loads gives a good combination of pressure/velocity ratio while maintaining good ignition characteristics. 700X is slightly faster as I recall, but there are still some good loads for it in reasonable pressure ranges. I have mostly loaded Hercules/Alliant powders for shotshell use with Green Dot being my favorite for my old ones. It is of a burn rate very similar to PB, but usually less expensive than the DuPont line.
