Also, many of these guys are supposedly experienced reloaders and gunsmith types.
They are indeed experienced.
If you go to the site and look at the energy stats for that cartridge, it gets a little easier to understand.
http://www.accuratereloading.com/577tyr.html
At the top end, this rifle is dishing out over 11,000 ft/lbs of energy. That's a 750 grain bullet at about 2600fps.
For reference, 50 BMG energy figures are in the high 11,000 ft/lbs range witha 750 grain bullet around 2750fps.
As I mentioned earlier, 50 BMG rifles are generally equipped with very efficient muzzle brakes and often weigh more than 40lbs.
The rifle in the video is probably less than 14lbs and has no muzzle brake.