Bridging is when powder doesn't flow out of the powder drop (But you already knew that!), and second issue is when powder just sticks to the inside of the powder drop.

The two simplest answers are the same Vibration. One is a small vibrating devise firmly attached to your powder drop (two friends did this to shotgun presses, one used a small pink marital aid, the other use the vibrator from a beat up Bark-o-Lounger) and this idea worked well for several decades. The other solution is what Lyman did over a hundred years ago with the #50 (and later #55) powder drop. "They hit it with a Hammer". There is a small door knocker like attachment that you flip when the handle is up and again when the handle is down. They called the thing a "Hammer". You can do the same to any powder drop, by rapping it with a screwdriver handle or a small hammer. Again, once when the chamber is filling and when the chamber is emptying.

I have a Lyman 55, but have used the screwdriver method on a Redding BR 30 and a few other drops. The Lyman is so fast, you hardly loose any time once you are used to it.

Ivan