Power Belts were designed a long time a go, I believe it was during the time when every one was using the at that time new 1-48 twist. I personally believe the 1 in 28 twist we use in most inlines makes them open to fast if you put more than 80 gr behind them, so even though they can be very accurate they are not at the top of my list. If you want a lot of info on them check out Ganders web page.
Most of use feel sabot-ed bullets are better but if you want to find an other conicals there are a number of them available, the FPB from Hornady is excellent and I have had good results with the heavier Bull Shop and No Excuses also the Thor and the Sabertooth. It is important to have confidence in what you use. Lee