I honestly shot 1,000s of ball out of my Walker over 25 grains of 3f Goex....No problems what-so-ever. Otherwise my Walker hit way too high.
The blackpowder air gap myth is an internet sensation and is parroted daily by folks that don't understand "Why?" the air gap can cause problems. So many false ideas and speculations of this, from "flash-over"... "instant detonation"..to the most silly "too much Oxygen!!"
Only when the column of powder is very long is there trouble with an air space. When a settled or compressed powder column of black powder is ignited from the rear, the solid mass of powder speeds forward as it burns away. Compressing the air in the gap between it and the projectile....there-by forming a bore obstruction situation.
This isn't even that easy to do in a lab. Western Powder was hired by CVA to blow-up some muzzloading rifles...They couldn't get it done with black powder and the airgap!!.. and had to go to smokeless
Schutzen guys have been adjusting the air gap in there rifles as part of load development for 100 years!
Enjoy that Walker!!! Awesome machine