Aherm. This one's not a full rifle as it's an Upper for the AR-15 made by Zel Custom. In the US, it's considered an accessory and thus will not require papers when purchased. The T2 is magazine fed using the 5-round .50 BMG magazine made by Accuracy International and its design was based on the feedback by law enforcement and firearms enthusiasts on the single-shot T1 made by the same company.

For an airsoft gunsmith creating an upper receiver for an airsoft M4 based on this would require more creative thought. As the .50 BMG magazine is mounted on the side like a Sten gun, there are no existing version 2 gearboxes. There are two gearboxes that would allow such feed: the M249 gearbox and the Version 7 Gearbox used by Viva arms for their Sten II Mk.II Silenced but fitting these into a receiver for Version 2 gearboxes would be such a chore that it might a need whole new gearbox design. Our guess is that it's much easier designing one using Gas Blowback technology and Ares Airsoft is the company that is known for making gas blowback rifles on the not-so-common rifle designs. But then if anyone who has a workshop and make some modifications on either WA or WE gas blowbacks, then it might work. I guess it makes sense using gas blowback magazines as the T2 is a a bolt-action upper for the AR-15.

Here are videos of a prototype of T2 before it got officially released last 22 August 2010. More details of the Tactilite T2 from Zel Custom after the videos:

The Tactilite T2 .50 BMG upper for AR-15s is renowned for quality and accuracy at an affordable price.  Like the T1s, the T2 magazine-fed .50 BMG conversion kit for AR-15s is built around our unique "Gen-3" receiver, which is CNC-machined with an integrated scope rail from a single piece of hardened CRMO steel stock.  The magzine well and catch are heat-treated 4140 steel, for incredible strength and durability  Together with a free-floating barrel, this makes the Tactilite T2 inherently more accurate and stronger than alternatives costing hundreds or thousands of dollars more.  With our unique "double-finish" parkerizing and CeraKoting process and you've got a steal-deal.

Available in three models, with choice of barrel lengths and contour.

• Ultralite is our value model, featuring a Mossberg-made barrel with U.S. mil-spec size chamber. 
• Duty is our LE/MIL model, featuring a Lothar-Walther barrel with a hybrid match / mil-spec size chamber. 
• SuperMatch is our competition model featuring a stainless steel Lothar Walther Super Match barrel with a match chamber