Use real black powder in that flintlock. Triple 7 will work but will have slower ignition. If you were priming the pan with that stuff i am amazed you got it to fire at all. Real black lights off at 300c andTriple 7 is probably around 370c; I am surprised a flinter can do it consistantly.If youwant the velocity advantage of Triple 7 then buy Swiss brand powder in 2f grain size. Goex will be around 170 f.p.s. slower than a Swiss 100 grain load. Ditch the Triple 7 and shoot real black. There is no advantage to Triple 7 in a flinter. Consistant ignition and velocity is what you need to shoot flinters accurately and nothing is better than real black powder. Prime with 4f, barrel charges should be 2f in a .50 but many people use 3f. The 3f is hotter, faster and will give higher pressures. If you use 3f it's harder on your barrel and if you don't swab between shots there will be more standard deviation in regards to velocity between shots.

The best accuracy with sabots comes from a clean bore. Here is how to do it. Swab the bore clean until your dry patch is clean,drop your powder down the bore, put your bullet in the sabot and use a short starter to drive itin about 5" or so, use theramrod to seat it on the charge with the same pressure every time, now take alighty lubed cleaning patch and run that down the bore and back out. No gobs of lube just a thin coating; thats it. If you insist on using triple7 as a main charge don't use any lube after the sabot is down the bore because it justaids the formingof a crud ring which isconsistant with the use of Triple7 substitute powder. A compressed charge will yeild more velocity but ignition is not as fast or consistant in time frame.Leave a little air between grains of charge but thesabot must be on the charge.A light crunch is best.