The apotheosis of bullet weaponry, the boltgun is a perfectly-crafted firearm gifted only to the Emperor's finest. Boltguns fire shells which explode shortly after penetration, inflicting massive tissue damage.
"Dude, my massed S4 AP5 boltguns totally pwunzorised your lone Grot" -WH40k nub
"Dude, my S10 AP2 Demolisher Cannon just totally pwunzorised your entire squad of boltgun-nubs" -Slightly more fortunate WH40k nub
To thoroughly creep out women on the internet, become a sexual predator, and ask underage girls for pictures of their tits. Any of these three means you are a "Boltgun"
Dude did you hear? Tyler pulled a Boltgun, he asked someone's fifteen year old girlfriend for pictures of her tits man!