I did some research to try and ID the rifle; the 'SIG Sauer SIG50 50BMG' seems to be the perfect match, but if anyone knows for sure then please correct the tag.
FYI if you are wondering when the TAC-50 and SIG-50 look so similar, a bit of Googling gave me this
SIG 50 sniper / anti-materiel rifle is a joint effort of the US-based branch of the famous international SIG SAUER arms making company and another US company, McMillan rifles. (...) Not willing to reinvent the wheel, SIG SAUER managers turned to McMillan with request to develop such rifle to their specifications. As a result, SIG 50 rifle was born as a modified McMillan TAC-50 rifle, slightly lightened and with modified ergonomics.
