Without having the rifle in hand and trying shooting it, very difficult to diagnose the problem with ignition you are describing. Lot of tips so far (bank, don't bank, lots of prime, little prime, pick, scream, cuss, etc.) but you still seem to be having issues. My flinters, especially the longrifle I shot for 40+ years gave/give good ignition. They are not fussy on how I prime although my preference is a thin line of 4Fg along the bottom of the pan. The longrifle will even fire about 50% of the time with NO prime in the pan. You have, supposedly, a good lock. Before sending back, I hope you can enlist the help of someone near you with flintlock experience to look at the rifle and maybe get it working for you. If not, talk to the builders again and try to find a solution before shipping. Good luck.