huntitall,
In my experience, 777 pellets are not reliable in the Huntsman. The breech plug is designed for loose powder and there is no alternative except the .25 ACP breech plug. The Huntsman will set off Pyrodex pellets reliable, due to the real Black Powder bonded to the ignition end.
PowerBelts need a good ignition every time in order for them to obturate (belly out) into the rifling. Although the PowerBelts are generally accurate, I am not a fan due to the poor performance I have witnessed on big game. Much better choices out there IMO. SST/Shockwave saboted bullets have done wonderfully for me, but with truly big game I use all lead conicals in the 400 to 460 grain range. The Bullshop or No Excuses would be my recommendation.
Did you swab out all the oil in your barrel and fire off a couple primers before loading? Oil in the flash channel can make a rifle hang-fire or mis-fire. Alcohol will remove the oils in the barrel, but always pop a couple primers to clear the flash channel.
My best advice would be to drop the 777 pellets and get some loose 777 powder. Loose is much more economical to shoot and you can tailor your loads.