Ultimate compact AR has a barrel length of just 2″
This SBR AR-15 has been cut down so far that the gas block actually extends PAST the barrel. The barrel is so short, the ammunition it fires is longer by more than 1/4″. You can see the tips of the bullets extending past the barrel in the video. Surprisingly there is virtually no flash since a great deal of propellant is essentially wasted and can be seen as black smoke leaving the rifle.