LIL'GUN™ is the powder used in the .17 HRM. It's mainly a slow burning shotgun and magnum pistol powder. Being slow burning, it needs all the barrel length it can get to burn completely and deliver top velocity.
That's not to say that the .17 HRM wouldn't work in a shorter barrel,,it's just that you won't get what you pay for out of the round in a shorter tube.
