Well seeing how the forum is messed up again and wont load any other pages, it allowed me to make a new one and worked! Okay i just finished up shooting with powerbelts:
Traditions kentucky classic .50 flintlock
70 grains Meteor FFFG blackpowder
295 grain arrowtip Powerbelt.

First 3 shots were taken at 25 yards, First shot, dead center, a tiny tiny bit high and clips the black bulls eye, second shot hits low and to the right " see pic", After swapping, i load #3 powerbelt and take a shot and it highs right above #1 shot. I was very happy with that so i moved out to 50 yards after swapping the barrel with a few patches.

First shot at 50 yards hits dead center and 3" high, second shot hits 3" high but 2" to the right, 3ed shot i aim at the bottom of the orange and it hits dead center and clips the top of the orange. I'll have to buy some more powerbelts before i can try out 75 and 100 yards. This was a fun day! I may have a new elk load for this january. I was suprised they shot this well. I guess the real test will be once i move out to 75- 100 yards. This flintlock is really giving my inline a real stiff compitition. That Meteor powder is really fowling up the barrel so once im done with this stuff, i'll be buying a few lbs of goex 3f.

So to all those who wants to know if They can use powerbelts in a 1:66 twist barrel, You'll have to buy some and try it out! They worked great in mine so far.