It's the camera!
Keep the camera on the pistol when shooting to increase reliability.
Seriously though, looks like a neat idea but poorly done - not all the bugs worked out.
If it were mine, I would
not decrease the the relative size of the "anvil" - less surace area wouldn't necessarily improve the impact. I would instead look for a way to increase the hammer impact by tweaking the spring.
As for the BB not leaving the barrel, hm. Might improve with break-in, maybe a teeny bit of lube on a few to see if that helps.
Always enjoy your videos, thanks.
EDIT: Just had an afterthought - you might tyr lubing the tin of BB's with something like Lee Liquid Alox. Put a smidgen of lube in the tin, put the lid back on, then rattle 'em around abit to distribute the lube. Then they'd be ready whenever.
If Alox is not a suitable BP lube, a few drops of olive oil might be better.