I have an Encore 209X50 and haven't had a chance to shoot the powerbelts thought it yet. I settled on the Hornady XTP 300 grainers over 100 grains of loose Triple 7. I was getting 2" groups at 100 yards which was plenty good for me.
To top it all off I just killed an 8-point buck yesterday, Arkansas' opening day of early muzzleloader season. The bullet entered the front of the left shoulder and exited the left side. Deer was quartering toward me. When the deer was gutted, both lungs and the heart were mush. At the taxidermist's I was able to get a little more info on the bullet performance. After the deer was skinned I saw that the entrance hole was a perfectly round hole and the exit wound was about the size of a golf ball on the opposite site. There was a piece of the jacket (one petal) and a cunk of lead lodged in the hide at the exit site.
The deer dropped on the spot, which is what I was after. I intended on going with shoulder shots this year instead of the traditional lung shots. I'm red-green colorblind so tracking a deer is not my favorite pastime, especially with no snow to help. That's why I went with a heavier bullet. I'd go with something around the 300 grain range if you can. Little better penetration if you end up having to pass through bone or more of the animal, such as my quartering shot.
Ranger413