Vent pick and picking the vent.....

[Daryl]

I've never found out why some folks blow down the barrel after firing.  Is it to get rid of the smoke that might be lingering in the barrel?  By blowing down the barrel, you are introducing moisture into the barrel.

You are going to be reloading right quick, and it seems that the ball, inside the lubed patch, is going to blow out all the smoke and/or moisture right out the touch hole.

I do stand ready to learn.

True - with a large vent hole, when using 3F as the main charge, some powder is lost out the vent as well.
Just once, load with the frizzen closed as was done by EVERY military during the flintlock era. Upon opening up
the frizzen for priming, see if it self-primed.
A couple granules is nothing. A full pan means you need a new vent liner, or a more coarse powder.
The amount of powder lost will vary each time the gun is loaded.

[MuskratMike]

After attending and calling the match at many large BPCR matches where they blow "up" the barrel with blow tubes. It is to add moisture which softens the BP fouling. They also wipe after every shot. I am not promoting or bashing either this is just an observation.
I do blow down the barrel after each shot with my flintlock. #1 to show there is no post ignition crud blocking the vent that will require vent picking and #2 to soften the fouling. I do believe it helps in slowing the fouling, but this is just my personal experience from 40 years of shooting and has no scientific proof backing it.
"Muskrat" Mike

[Daryl]

I know people do that to soften the fouling. In my own case, I've never, in the last 40 years of shooting BP, had fouling that
needed blowing on as it never builds up & it's already damp from the shot - no matter the climate.  My loading practices in 5%
humidity are identical to that in 90 to 100% humidity. In high humidity, I usually have to wipe out the pan before priming.
Each to his own, though. I know there are fellows who need to wipe their bores after every shot and there are guys who need to wipe
the bore every 3, 4 or 5 shots. Such is life. There are also guys who want to wipe their bores after every shot. I just don't happen
to be one such shooter.