Grabbing the cylinder of a revolver to stop it from rotating sounds like it would be feasible, but in practice it is very difficult to maintain a grip on a snub. With one hand it's nearly impossible. You pretty much have to get two hands on the gun and in the case of someone with a knife or other weapon, that's obviously not happening. It's actually extremely difficult to maintain a one-handed on any handgun suitable for concealed carry in the context of an actual fight over control of the weapon. In regards to being attacked with a knife(or any contact weapon), going immediately to the gun is rarely the best option. Someone determined on doing you harm doesn't generally announce their intent from across the street. If someone is truly wanting to stab you, they will attempt to get really close first. You can try to quickdraw or backpedal like in the video, but you're most likely getting shanked either way if you go that route. Either explode off the X pointing your toes in the direction you're wanting to go to create a lot of space quickly or you'll have to use unarmed skills to defend initially to effectively get to the gun or both. An MMA fighter armed with a pen attacking an older guy with no skills or training aside from static range shooting or a basic NRA or CCW class....I'd put my money on the MMA guy in a 0-5 feet scenario.