I think blowing down the barrel can be a bad, and dangerous habit. If you can forget to put the powder down the barrel first, then the patch, then the ball, you can also screw up, " Shoot the gun, Then blow down the barrel". The first screw up introduces to the exalted club of dry ballers; the second can get you killed. It ain't worth it.
I stopped blowing down the barrel years ago, when I realized that I was teaching a dangerous habit to observers who had not taken the years of practice to learn to be safe. I have used a pre-cut patch wet with a little saliva to wipe the bore, and put out any embers for more than 15 years, and have never looked back. On really humid days- I can tell when humidity is a problem, or I have put too much spit on the patch( it happens), when the gunk on the patch comes out shiny and greasy looking- I run a dry patch down to fish out any gunk I have pushed to the back of the chamber. That keeps the gun one shot dirty all day long, and I have no problems shooting regardless of weather. Accuracy also stays constant.