I've been wanting to do this one for a while, so I figured I'd throw it out there. All the G4's get their own designation. What do they all mean?
A1 -- Generally M4 length gun with smaller, square RIS unit, and no front sight on the barrel
A2 -- Shorty guns made for CQB (The Extenzor is obviously an offshoot, but makes the list because of its Noveske sound amplifier)
A3 -- Characterized by round hand guards, and a flip up sight, mounted to the barrel
A4 -- Yes, even we are not immune from Magpul mania
A5 -- We chose this model to highlight some of the excellent, affordable URX rails that have become available recently
18 -- The major design element of these guns is the revolutionary MK18 RIS unit
PWS -- Uses the Madbull PWS Diablo kit. On the real gun, the kit offers stability and accuracy never heard of from such a short barreled M4. On the airsoft gun, it just looks mean.
DMR -- Designated Marksman Rifle...in other words, long barrel, tightbore barrel...the perfect, mobile, sniper platform
Tactical Carbine -- Carbine length barrel with a full stock
More designations will probably become available as time goes by. If I missed one, PM me.