Flintlock is a learning experience. Caplock is almost like firing a cartridge weapon, hence lots of beginners like it. With flintlock, you need to develop your skill until it's almost like firing a cartridge weapon. It can be done but it takes some learning beyond measuring a charge and seating a patched ball.
Big G is right, you learn how to gauge your rock, how to keep it clean, sharp, and functional. We recommend that shooters fire a caplock for a year before they go to a flintlock because you learn the drill of loading a muzzleloader without fighting with making fire. A caplock is (almost) guaranteed fire on every shot.(compared to a flint!)
What makes you say that a flintlock would be more accurate than a cap lock. These differences are only the manner in which the main charge is ignited. The accuracy is a matter of the barrel, rifling, crown, and projectile fired. Many find that cap locks' are more accurate for them due to a quicker lock time.
Sorry, Meddac19, the flinter's are usually used by more experienced shooters, who, due to differences in flash time due to weather effects on muzzleloaders, practice better followthrough. ( meaning they hold on the target all the way through the shot.)
Flintlocks have external ignition, which makes them more prone to gum up in humid conditions. Experience teachs you how to keep shooting. (sometimes other's experience helps too!)
Caplocks inherently have the a weakness in the turn the flash must take in travelling from the cap down the nipple to reach the powder charge. This area can plug up in moist conditions or get wet and cause hangfires. (I used to call this flintlock practice!)
I thought at one time that a matchlock would be more challenge than a flintlock, until I shot flinter, and realized that constant fire(in the match) was not the challenge that making fire with a rock for every single shot was.
Ultimately, yes, it is the rifling of the barrel and the trigger and the sights that helps determine the accuracy of the rifle; but do not forget that in blackpowder shooting, where the shots are all offhand, the human element cannot be discounted, and the best shooter will prevail at the end of the day.
nomadboi and enkindler; The Gunworks in Springfield Oregon has a good stock of the holy black, as well as everything else you might want... They sell online or are right off I-5 if you are headed south.