Sounds like one of those 20 mm. Finish anti-tank rifles you could buy by mail order in the 1950s. Calling her profound ignorance of firearms stellar is a total understatement. Indeed, the only way even to illustrate it is to quote her directly and in context.
Like Clint Eastwood used in Thunderbolt and Lightfoot.
I suspect she saw and held a bolt action or semi-auto rifle that fires .50 BMG. A firearm that is too heavy and wayyyyy too expensive to be used by nutball shooters for indiscriminate killing.
Not to mention that the recoil would probably kill the kind of soyboys who do most of these shootings the first time they fired it.