What are the orange flakes sometimes caused by? Not always there but only "Sometimes" ?
Normally its little red beads. If I dug deep enough I could find Bill Knights explanation of this. But its really not something that can be fixed or particularly worried about. Charge weight, caliber, weather, powder brand. ? Flakes? Of any color… Some powders in some guns/calibers at some charge levels cause flakes. They can be a huge PITA and cause misfires etc with some breech designs, even a plain breech. So some either pick the vent or put a pick in it when loading. I use Swiss for this reason. My Nock Breech design 16 bore will misfire in 2-3 shots with Schuetzen at the same charge and granulation size. Never tried anything else. Then priming must be worked through the vent to get the fire lit. Swiss never does this.
If you find the right patch combination you “might” be able to shoot a ball cast from lead free solder but it would likely need to be a little undersized compared to pure lead. Barrels with wide shallower (.008”) or so and of course the naroow lands will work best with hard RBs. Might need a over powder patch and likely linen patching. But this alloy is pretty pricey. Pure tin might work as well and light be softer than the solder which is often alloyed with silver and copper. Tin can be bought from those who supply bullet metal to brass suppository gun shooters/bullet casters. Try Rotometals dot com. Its worth a try. I would use on of the graphite spray mould coatings. Dunno how “sticky” this stuff would be.