Wow! Three pages of comments in one day!
Gavin, please re-read Grenadier's post, #46. That's what you need to know.
I am not a reenactor, but I thought for a time I might volunteer at the Castillo de San Marcos in St. Augustine, Florida. On certain days, they have living history volunteers dressed as circa 1740 Spanish Marines performing musket drills with volley fire, as well as cannon drills with blank loads. They have a one-day "School of the Soldier" and a two-day "Cannon School," which are required for volunteers participating in the shooting activities. One thing to keep in mind is that all of this, training, living history, and shooting, is sponsored by the National Park Service (NPS). You can bet all procedures were carefully vetted.
With the musket firing, every participant is required to have a flash guard and a leather hammerstall (frizzen cover) installed on his firelock. The half-**** notch is the musket's "safety," and proper function is verified before every drill or demonstration by placing the lock at half-**** and suspending the musket by the trigger on your finger. Considering these military muskets (I have a Charleville) weigh in excess of ten pounds, the "trigger pull" at half **** is pretty stout. We would also "ping" the metal ramrod against the face of the breech plug to verify the bore was unloaded and clear.
The musket drill was basically a sequence of commands. There is no need to go through all of that, but the pertinent details are that the hammer stall is in place and the gun is at half **** when the paper cartridge is opened. You prime the pan from the cartridge and close the pan. With the musket butt placed on the ground and the gun leaning so the muzzle is forward, not in your face (or anyone else's), you pour in the powder, crumple the paper cartridge to use as wadding, then ram the wadding down, using only your thumb and forefinger on the ramrod, which is then quickly removed and replaced in the gun. You remove the hammerstall and bring the lock to full **** when commanded to do so. Even after the shot, there is a procedure to follow. Considerable time elapses between volleys, so there is little chance of a latent spark or "cook off."
So, as sanctioned by the NPS, you prime from the cartridge before loading the main charge, but with the lock at a secure half **** and with a frizzen cover in place, so even if the **** drops unintentionally, there will be no spark. At no point is the muzzle pointed anywhere near your person or your face. The cartridge paper is used for wadding, which requires ramming, but the ramrod is manipulated only with the thumb and forefinger, and ramming and extraction of the rod is done quickly. There is a specific sequence of commands for replacing the ramrod in its place, minimizing the possibility of a "shot" ramrod. There are no opposing lines of fire at the Castillo, and no projectiles.
Following the musket drill, risk of accidental discharge is minimized, even with priming before loading. However, you do not deviate from the drill... You follow every step, in correct sequence.
For the record, I have shot paper cartridges loaded with ball, on my own, but I prime after loading, from a priming flask.
Notchy Bob