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.