umm you guys...I hate to burst your bubble, but
a) that was no sniper and
b) that was a plain old M4A1 with RIS and an Aimpoint. Suppressor was same size and shape of QD, but without stamped holes in suppressor sleeve. There are several Quick Detach sups out there, but the one I am speaking of is the Knights variety.
The sniper rifle in TOS, as with many other SEALs and military personnel, was an M14 variant. Possibly an M21, but there is no external differnce.
On another note, snipers sometimes use an M4 or a variant of, instead of the primary M14, M21, M24, M82, M40, etc...
The spotter also uses them sometimes. When this is the case, the weapon looks exactly like any other pimped-out M4.
Cheers