 Pipe guns are easy to make, easy to use and can easily fire 12 to 15 shots per minute.Flare guns have also been converted to firearms.This may be accomplished by replacing the (often plastic) barrel of the flare gun with a metal pipe strong enough to chamber a shotgun shell, or by inserting a smaller-bore barrel into the existing barrel (such as with a caliber conversion sleeve) to chamber a firearm cartridge, such as a .22 Long Rifle.