1hunter - I have tried 777 in both loose powder and pellets in inlines and sidelocks and with bad results. Its nasty and didn't perform very well. I am not the only one around here that has had the same results and have seen several barrels that it has eat up (could have been bad barrel stock), but seen some that it works for. Also 777 has a higher energy per volume than regular Pyrodex and for the most part from what I have picked up on from time spent on the range over the last several years is that 777 burns better with a magnum primer especially in the pellets. If you are going to go to shoot loose powder I would suggest Pyrodex RS or Select and use a non magnum primer. The magnum primers are better used with pellets and sticks as these are dense and do not compact like loose powder witch leaves small air channels around the load. If you want to see what i'm talking about, take an inline with removable breach plug and load just your bullet then take a magnum primer and shoot it, look how far it moves the bullet down the barrel. Then load your bullet again and use a standard primer and compare. We done this one day when I switched from a standard primer to a magnum primer shooting the same loose powder load in the same gun I had been using for years and it wouldn't group. Also done some research on it. End result is that a magnum primer is pushing the powder and bullet down the barrel as the powder is still burning witch in turn you are loosing the compaction in the charge you need for a good burn resulting in bad groups. Also loose powder will allow you to tune your gun as yours may like something better at say 90 or 110 for example. Muzzleloaders are no different than centerfire rifles as some like certain powders, loads, and bullets.
AROD - you may have to try several different powders, loads, bullets, etc till you find what works. Not shot the Vortek or seen anyone with one to give you a starting point. Just hang in there and keep trying. Also if you are using a tight fitting sabot you may have to swab the barrel after a couple of shots or every shot as the plastic from the sabot can clog the rifling in the barrel.