I pass this one along for your edification. According to the text that came with the video, this is one of three .950 JDJ rifles made by SSK Industries of Ohio. This is the lightest of the trio, the carbine version, weighing in at a negligible 50 pounds. The bullets, which appear to be lathe-turned bronze, weigh 2,400 grains and are pushed at 2,100 fps by 240 grains of powder. The .950 JDJ develops 25,400 foot pounds of muzzle energy and 277 foot-pounds of recoil.
To put this in perspective, the .700 Nitro Express, which is made by Holland & Holland and is generally considered to be the largest civilian cartridge extant, fires 1,000-grain bullets at 2,000 fps with 8,900 foot-pounds of recoil and 118-foot-pounds of recoil. A friend of mine has shot a .700 offhand, and assures me that the thing is unmanageable.
Or to look at it another way, the .458 Lott, which is the most powerful sporting cartridge I know of that can be used by a sane person, shoots bullets that weigh roughly 1/5 of the JDJ slugs, develops ¼ of the muzzle energy, and ¼ of the recoil.
Enjoy, and be glad it’s not you doing the shooting.