My major addition to standard rules, which seems to often be ignored with BP:
Never put any part of your body in front of the boom tube, once a powder charge is in place.
I know this seems like it fits with the 'standard' rules, but people ignore it too often with muzzle loaders, since you're not dealing with cartridges.
Too may people stick their faces, arms, and hands over the starters, ramrods, and even loaded bores. ...Because it's "just a muzzle loader".
I even saw a notable member of this forum, whom has a YouTube channel, do such (in all aspects) in one of his recent videos (last 6 weeks, or so).
"Well, I just seated that projectile on the powder charge. Let me put this ramrod back in place." ...While putting his hand, arm, and FACE in front of the muzzle.
...
That being said... I am going to go against the grain here and add rule number 3,712:
Do whatever you feel is safe enough for the risks you are willing to take.
For example...
There's a rule with muzzle loaders, 'never over-pack the powder charge'.
This is often seen as people "bouncing" the ramrod off the projectile after seating it.
I was taught to do this. I found ignition to be very unreliable without doing this. To this day, I will not pull the trigger on a muzzle-loader unless I can bounce the ramrod out of the barrel to verify that the powder charge is packed tightly.
The average BP shooter says it is because there is a risk of compressive ignition and kaboom. It is true. No denial. But it is infinitesimally small.
Competition shooters will tell you that it is because this results in variable compression and erratic results down range. I disgree with that being a justifiable argument, since all methods of packing have variable results.
And I don't put any body parts in front of the muzzle (other than fingers handling the ramrod from the sides). And I've found tight packing to be necessary for reliability.
Yes, bouncing the ramrod might deform Minie balls or "Plains Bullets" with hollow points. But for round balls (which is about all I shoot), it's a non-issue for me. The risk is far lower than the reward.
I think some BP rules are a little over-exaggerated, hyper-inflated, or just Fudd lore.