Your rifle fired because the cartridge rim is held by its "seat" - a groove, or perhaps the rear face of the barrel. The rim was seated solidly, the bolt closes, and the firing pin strikes with enough energy to fire the primer, which ignites the powder, etc. In the instance of a rimmed cartridge like a 303 British - the condition of the chamber has not much to do with whether the cartridge will fire or not, so long as the cartridge can fully seat in there.
However, upon firing, the case is going to expand in all directions and "seal" and conform to the chamber walls - should actually "grip" those walls for an instant - to direct the pressure against the rear of the bullet that is moving up the bore. The brass case should relax slightly once the bullet exits the muzzle, allowing you to withdraw the fired case from the chamber. Your video is showing instances where that bolt opening, which is also the initial movement of extraction, did not happen smoothly, like it should.
Those "lumps" that you highlighted are no doubt that brass flowing into the divot created within the chamber. Chances are good that most resizing dies will "smooth" them. However, as has been posted multiple times on this site and others, your more pressing concern about reload-ability would be "incipient" (about to happen, but has not happened yet) head separation.
You will find that by sharpening the end of a piece of a bent wire, or straightening out a paper clip, and feel inside your case - just in front of the solid case head - chances are good that you will discover a ring in there - the case walls, right there, have been thinned and the head will separate and come off right there. I saw no evidence that you accommodated the "head space" with your initial firing of the factory case - without doing that, the case stretch has been done and can not be undone. 303 British military design was to chamber, fire once, extract and eject and on to the next cartridge. Those designers a hundred or more years ago gave not one wit of concern about re-loading that case - up to us to figure that part out today, using what they had designed.