The gun control movement has a problem in the US. The overwhelming majority of Americans believe in the right of the people to own guns, and don't support the gun bans that big players like the Brady Campaign, Violence Policy Center, and Mayors Against Illegal Guns want.
Or rather, the overwhelming majority of Americans believe in the right to own guns, but... They have some reservations. Maybe they're uncomfortable with concealed carry. Maybe they're mostly cool with concealed carry, but not in some places. Maybe they only believe in private ownership of sporting guns, but not guns for self defense. Gun controllers exploit all these reservations, but the one that bears them the most fruit is the widespread perception that normal guns are fine, but there are some guns out there that're much more dangerous and need to be controlled.
Feeding that perception has gotten the anti-gunners one major victory, the National Firearms Act of 1934, which (among other things) placed heavy restrictions on machine guns. They've maintained the overblown fear of full-auto for three quarters of a century now, even adding more restrictions in the 1980s, but they have a different problem: now that they've succeeded in banishing machine guns, all other firearms are more or less the same.
For all the electronic warfare we've seen between the Browningites and the Gastonians, guns today are essentially unchanged from guns a hundred years ago. Improvements in materials sciences have made some of them marginally lighter and more carryable, marginally more durable, and marginally more accurate and easier to accessorize. And the small refinements can make contemporary guns more desireable to the modern gun owner. But in very real terms, the guns of today are no more deadly than the guns of 1934*. This means the gun banners have had to essentially manufacture a perception of deadliness out of whole cloth. The greatest success they've had was the "assault weapons" ban, a huge topic unto itself, but since the AWB has gone out with a whimper, they're reduced to manufacturing fear in some ways that stretch the imagination very, very thin.
One of the more common is their attacks on "50 caliber rifles", by which they mean rifles chambered in the very powerful .50BMG cartridge. These rifles are extremely powerful, but they're also impractical criminal weapons for a variety of reasons, which we frequently prove by pointing out that, in real life, they simply aren't used in crime.
In an attempt to refute this point, the Violence Policy Center circulates their exhaustively researched list of crimes committed with .50BMG rifles. It gets the desired emotional reaction out of many people: your eyes start to glaze with the volume of incidents, and you think "damn; bad people use these guns".
But look at the situation rationally:
A well-funded anti gun group has worked to find for every available reference to .50BMG rifles used in crime. As a result of this research, it's found a grand total of 34 connections to any crime whatsoever. Almost all are simple illegal posession by a felon or drug addict, with no actual violent crime taking place. At least one "crime" is a failure to comply with state "safe storage" laws, which the Supreme Court has suggested are unconstitutional. Several incidents are cases in which a person commmitted a violent crime, and a subsequent search of his home turned up a .50BMG rifle, indicating that when he went out to harm people, he deliberately chose to leave the .50 at home.
There are four actual violent uses of .50BMG rifles cited. In only two of them were the guns actually fired. There's no indication that anybody was killed in either shooting.
And this is for a cartridge that's been manufactured since 1921.
If you truly believe that restrictions on guns can reduce the 13,000 homicides with firearms that happen each year in this country, going after a cartridge responsible for a third of a crime per year and a grand total of zero criminal homicides is a pretty odd policy.
It's factually incorrect to say that no .50BMG rifle has ever been used in a crime, but saying that they "aren't used in crime" is just as valid as saying that jews don't murder Christian babies. Yeah, it's probably happened once or twice, but you're responding to wildly hyperbolic accusations. In that context, the difference between "never" and "at a microscopically low rate" is academic.
[* - The main exception that springs to mind is modern hollow-point ammunition, which dramatically improves the effectiveness of small caliber handguns. In practical terms, though, this only brings them closer to the power level of larger caliber handguns, which have also been around forever. "Handguns" aren't made deadlier with hollowpoints.]