I hear folks speak of "bumping" a powder drop when using it? What does this mean? When I use mine, I always tap it a couple times on the side when flipping the lever? I didn't know if this was the same thing. Inquiring minds want to know.

I use the term to mean hitting the upper and lower stops with a bit of force when working the handle. Not really hard, more like a good firm tap.

Start at 4:55 for the next 15-20 seconds, what he is doing is about how hard I bump it. Fwiw I use an RCBS Uniflow as shown here.

I do a double bump at the top and bottom. It has just become a habit.

Lyman had this figured out years ago on there No 55 when they had a knocker on there measure.

Hit it hard on up and down stroke.

Bump or don't bump. As long as you do whatever you do consistently, you will get consistent results.

Now if you want to really get into the realm of black magic, inquire about "bumping" shoulders.

Knockers are meant to occur in pairs.

Got this one figured out. Had to figure it out the hard way when I first started loading years ago.

This.
I call it a "tap tap" on each end of the stroke. Different words/same thing - it works consistently.

I think it was in the RCBS instructions, but I lost those 40 years ago.

I use a Redding BR-30 and I do not tap, knock, whatever. I grasp the throw handle in such a way to make a slow, high torque back and forth motion. This avoids vibration and bumps when throwing long kernel extruded powders. The handle doesn't stop, it just shears right through.

I do the tap, tap....only because I cant break myself of the habit. When I try not to tap, I end up putting a tap or two in there somewhere and the charges get a bit heavier.

As said above, consistency is key.