Starting with a clean rifle, is your 1st shot a misfire, or do they start occurring after your 1st shot? If only after your 1st shot, recharge the rifle, rap the opposite side from the lock a few times, with rifle tilted at an angle, muzzle up, to drive powder towards the drum. Do this before ramming home your bullet. If you get a misfire [after loading your projectile], wait a minute and then pull the nipple. If you see powder in the drum or snail, you have a nipple/cap/powder ignition problem. If not, you have a plugged flash channel and no powder is getting under your nipple, causing hang or misfires. Trickle enough powder into the drum to fill it up, run a pick through the nipple, put it back and try another cap. If that doesn't fire, it's a bad nipple, caps or powder.
I use t-7 and it makes a bit of a crud ring, near the breech, on every shot. I swab between every shot because I hunt, and all my 1st hunting shots are clean barrel. If you don't swab, there is a good chance your next bullet or prb will drive the crud into the flash channel. If you do swab, you will feel the crud ring. I use avocado oil swabs and work off the ring with a few strokes, with the hammer on half cock to allow venting. I then flip the same patch, give it one more swab and pull the patch out really fast so it pops at the muzzle like a champagne cork. This should create enough suction to clear the channel for the next load. It has worked great for me and all I use is t-7. 2 Traditions Hawkens and 2 TC Hawkens. The patented breeches [TC's and others like yours] are really finicky about this, but my other rifles are subject to the same issues if I am not careful.
Avocado oil is pretty high temp and does a good job of breaking up that ring. Just enough to dampen the swab, without dripping saturation. I buy it in spray cans and lay all my patches out on a cookie sheet and then store them in a plastic tub. Try whatever the real gurus on here tell you, and see what works best for you. Spit can work well for target shooting, but is a no go for hunting, especially in freezing weather. And it doesn't match the lubricity of my clean barrel load for accuracy. [I really don't want spit in my barrel for extended periods of time anyway.]
If you don't do something like this, besides misfires, sooner or later, as the ring builds up, it will prevent you from seating the bullet on the charge. And that can be a lot worse than a misfire. [Look up "ringed barrels"].
Also,I can't speak about Investarms, but the TC's really don't seem to work well with really tiny flash holes in the nipples. They prefer something between .028 and .034. I use the Knight Red Hot nipples in my TC's. Not to be confused with the vented Hot Shot nipples, which don't work at all for me with t-7. The Traditions don't care, and love their factory nipples, until the flash hole is too big. Another story, but anything beyond .034 is trouble territory. Good luck. SW