The .577 TRex I have not got any data on but .577 calibre rifles like the .577 Nitro Express are designed to work on dangerous game in Africa....usually Buffalo or Elephant....it is meant to be able to stop a charging animal. The rifle shoots a 650g bullet at velocities of 1850fps to 2000 fps. A 600 N.E. or Nitro Express shoots a 900g bullet at the lower end of the above velocity band.

The kick on these is more of a "push" than a "slam" .....which you get from faster cartridges which shoot heavy bullets such as a .50 Browning or ".50 BMG" which shoots a bullet of 709g at 2300 fps. Rifle weights also differ considerably with the .50 BMG being a much heavier rifle....but the video is misleading...it is possible to shoot the .577 or indeed the .600 N.E. stood up and without dropping the rifle and hitting a paper side plate at 40 yards with iron sights using a light weight rifle of similar weight to that in the video ......firing two shots in quick succession.

The people in the video seemed to be a bit inexperienced on shooting rifles of this type IMO....unless the .577 TRex is some wildcat case using .50 BMG velocities...but I seriously doubt it.