Hi,
Back in the 1830s, the British Board of Ordnance worked on developing and testing percussion ignition for their small arms. They did a lot of testing that compared the accuracy and performance of flint and percussion small arms under field conditions. Their results overwhelmingly supported percussion ignition with respect to both accuracy and reliability under battle conditions. The gain in accuracy was because of little loss of gas pressure from percussion locks and fast and hot ignition compared with flintlocks. However, they also noted that loading and then capping was slower than priming and loading a flintlock. They also noted that percussion guns performed much better during wet conditions. Nonetheless, the results were for shooting under battle conditions in which the guns were rough handled and little time was spent on care between shots. Today, we are not fighting battles with muzzleloaders and we usually have time to care for our guns, to clean vent holes, dress flints, wipe pans and frizzens, have coned vent liners in our barrels, etc. All of which helps make flintlocks very reliable. In addition, my impression is that flintlock shooters tend to know more about their guns and effects of weather conditions than many percussion gun shooters. Many neophyte muzzleloader shooters choose percussion first and their inexperience tends to bias results of comparisons with flintlock shooters. Anyway, the components in the ignition system are more accessible to flint shooters and problems are easier to fix compared with percussion locks and breeches. With care, flintlocks are easily as reliable as percussion locks and any loss of accuracy due to gas escape is probably very small provided ignition is hot and quick. Flintlocks are also just a lot more fun to shoot.
dave