250,000 vehicles in the US? That's an very poor estimate, as is the 25% of adults owning firearms.

according to the census bureau, in 2006 there were 48,000 deaths in motor vehicle accidents.

In that same year there were 13000 homicides involving firearms.

You can parse, twist and adjust statistics however you care to, but the end result is the same. you are far, far more likely to be killed by a motor vehicle than a firearm.