No,start with 70gr triple 7.
100gr triple 7 is to much powder with the Powerbelt,unless its the big 405,444 or the new 338 platinum
Why is 100 grains of Tripple Seven too much with a Powerbelt unless its a big heavy bullet?
Depending on the rate of twist in a given rifle, such as the 1:38 twist in my T/C Thunder Hawk Elite, it requires a full charge of 120 grain of Tripple Seven loose to stabilize 295 and 340 grain Power Belts.
I did however make the assumption that marlinman1's gun was a magnum muzzle loader that could handle 150 grain charge. My bad. If his gun is a standard 50 caliber then 110 grains is max for loose powder.
Start with 70 to 80 grains and work your way up till you find the charge your gun likes.