There’s a HUGE difference from being hit and staggered and being truly knocked or hurled backwards like happens in the movies. That impact gets spread out through whatever material blocks the incoming round(s) and then through your flesh.
Even a handgun round, something with low velocity, can stagger a person if it hits them in a ballistic vest. There’s force in the impact, which is sudden and unexpected. Any distance you travel though, would be a product of your own body’s energy as you try to move or correct an imbalance.
Being ‘knocked back’ like happens in films or other video games, is not at all realistic. If you take a shotgun blast to the chest, I don’t doubt that you’ll fall backwards, but no more than if I shoved you gently in the chest when you weren’t ready for it.
I’m not sure if I worded all that correctly. Basically, I’m pro-knockdown, but anti-knockback.