You don't need a holster to pack two barrels of power with the DoubleTap Tactical Pocket Pistol ($500-$800). Available in aluminum or titanium, and with or without a ported design, this double-barreled firearm measures just 5.5" x 3.9" x 0.665", and features a spot for spare rounds in the grip, a hammerless, no snag design, and your choice of .45 or 9mm compatibility.