I got the email, thank you very much. The article stats that the cartridge is 4.5" and is 1.135" at the mouth and1.180" at the head. So the gun is actually bigger than a true 1.052" 4 bore but much smaller than a true 2 bore at 1.35" diameter. It says it is the largest recognized sporting rifle in the world. I guess my 2 bore black powder with a 1.35" diameter and 36" octagon barrel will give it a run for it's money! According to the article, the 2500 grain bullets were rated at a TKO of 544. This is the bullet weight that they test fired. So at 1.180" diameter, the velocity should be right at 1300 ft/sec. My 4 bore gets 1480 ft/sec with 2000 grain bullets. So recoil looks similar to my 4 bore double.