Cave Johnson here,

After frankly too many hours of research into our turret units, we've discovered a small flaw... They're heavy as hell. No marine, war hero, home defender, etc. was willing to lug those things around. So, we went back to the drawing board and created this...

The Aperture Science™ Handheld turret!

Same devastating stopping power as our regular turrets in a compact, carry-able size. Our boys in the lab gutted a "less optimized" design and started from scratch. We cut NO corners. Just like our full size turrets, this device is capable of firing 65% more bullet per bullet by firing the entire thing, shell and all.

Though still in the testing phase, we sure they'll be ready in no time!
Grab your today and help further the knowledge of science!