I am thinking about trying powder coated cast bullets. One question I have is do they leave deposits of powder coating in the barrel and if so is it difficult to remove?

I use Bulletcorp coatings made here in South Africa, mostly for 44 Mag revolver and rifle
I just about never clean the barrels and they are shiny clean despite 100s of bullets going through them.

I am no expert. I powder coated some 390 gr cast bullets for my ex 470NE and did 2 coats of black. The coating was like a bonding. I did hammer tests and it was a duplicate of what you see on the YouTube. The paint is baked on and difficult to scratch even with a sharp chisel. The bore of the rifle was actually cleaner than when shooting copper jacket bullets like Woodleigh & Hornady.

if it's cured properly it doesn't leave anything behind.
if it isn't you can clean it out with acetone and a brush.
just make sure you hold the full 400 degrees for the full 20 minutes, after the powder turns 'wet'.

don't just set the machine for 400 and the timer for 20 minutes.
that don't work.