Again, swamp has a point but he dicks it up.
HCAW aren't the weapon of choice for crazy killers. We have exactly one instance where they were(unless you want to argue Aurora, at which point I'd say "He fired about 30 rounds with his HCAW and wounded/killed 70. That's not a majority" and move on). While it's certainly reasonable that one COULD kill more people with a HCAW than a handgun or a shotgun, that's not what they're using. It's reasonable that a car packed with explosives and detonated in a crowd COULD kill more people than a HCAW but, again, that's not what's being used.
So, to save swamp from himself, there's no evidence that a HCAW ban would reduce mass shootings.