briandg, I don't know for sure which picture you are looking at, but yes I have made a 2 bore. In fact, I am probably the 1st man to have made one as a "sporting rifle" in over 160 years. It was a Left handed back action rifle made for a man in Illinois.
The picture of the man being knocked down is firing a 4 bore and that with less then a full charge of powder. So you can imagine how the 2 bore would kick if it was fired with a "full charge”. However no one has fired it with such a charge. Such a folly would land you in a hospital in all likelihood.
2 bore is about the size of some of the old pack howitzers of the early and mid 1800s and when those guns were assembled they weigh about 300 pounds. The 2 bore sporting rifle weighs 22 pounds.
It's not hard to do the math, but the cannons at 300 pound loaded with a full charge (about 1600 grains of powder) would thrust them back about 4 feet.
If you cut the weigh by half you double the recoil.
So a 150 pound gun would have thrust back about 8 feet.
A 75 pound gun about 16 feet
A 36.5 pound gun about 32 feet, and so on
Shooting a full charge from a 22 pound gun would probably thrust you back and into the next world.
But with about 350 grains to maybe 450 grains of powder, the 2 bores can be shot from the shoulder. It's been done.