...what is it? During the final battle at Hoover Dam, whatever it was kept putting me into an uneding loop of stagger-animation that inevitably led to a game over. I'd pull up VATS, fire a shot or two, and then keep getting hit with this weapon/special ammo until I died, completely unable to move or pull up my Pip-Boy for healing.

Is this the riot shotgun at work here, or something else? It's annoying as hell, and seems to be bugged.

Ballistic fist?

No, I've experienced this with both NCR and Legion soldiers, and definitely at range. I don't think the NCR wields any ballistic fists.

Might be Brush Guns from Veteran NCR rangers?

But the Legon doesn't pack Brush Guns.

The Marksman Carbine and Cowboy Repeater are the only rifles I've found on both factions.

It might have been a frag grenade, but I've never seen anyone in the game throw one during both of my playthroughs.
I think it is the Marksman Carbine though, but there is nothing special to it.

AMRs? I got mobbed by about 6 centurions with those at short range...

anti material rifle? legion uses those...

The same thing was happening to me earlier and it was annoying the hell out of me. It is either the caravan or hunting shotgun, I'm 100% sure. At the very end I was fighting two NCR heavies who both had shotguns, everytime you get hit you get staggered. They can chain stagger you to death at times, can't vats, heal, shoot, or anything when it happens.

I hate it when that happens when I'am in first person as I don't know if I've been staggered or if its the crappy half finished game bugging out on me again.

Yes, this is it, exactly. They trap you in a stagger-chain and there's literally no way out but death. I'm wary to say this is a bug so much as a balancing issue.

Note that I've even had this happen to me in the middle of VATS - meaning I essentially spent the entire slow-mo portion staggering backwards until I died. It was pathetic.

I never realised this was a "feature" I thought my reload aniimation was just lagging when I finished reloading and still couldn't shoot for 3-4 seconds after during combat.

I have been chain knocked down by big horners....that was fun.

I agree that it's probably Legionaries with Anti-Materiel Rifles. I did the final mission when I hit level 30, and a trio of them charged out at me. I was using a Sniper Rifle so I just shot them all before they could get a clear shot at me. :gun: