Hardest Kicking gun you've ever shot?
I am not particularly sensitive to recoil. I say this not as a boast, just a statement of fact. My first handgun shooting as a youngster was with a .45 Colt, and I guess I just assumed recoil comes with the package.
I had a Colt New Service .45 Colt rebuilt to .44 Special, and did my first loading for this gun. Reading a lot of Elmer Keith, I went to his 250 gr Keith SWC and 18.0grs of Hercules (then) #2400 powder. This with the original plastic factory grips. My first outing with this combination left me with two bleeding gouges on my shooting had, one from the cylinder latch, the other of unknown origin. Then I learned about custom stocks.
Later, much later, I was introduced to the .45-70 in a Thompson Contender. This gun kicked hard, but it was fitted with those rubber grips that tried to skin the palm of my hand. Rubber grips and hard recoiling guns don't go together. They left the web of my shooting had raw and blistered. With decent wood grips, the kick is there, but my hand makes it just fine.
A few years back a shooter at the range asked if I would fire his double derringer, a .410 bored over/under that also took .45 Colt. The .410 wasn't bad, but my .45 Colts hurt my hand. The palm of my hand was sore the next day. This gun was stocked with Sambar stag, by the way. With my .45 Colt handloads, this has got to be my most memorable hard kicking gun. The .454 Cassul doesn't even come close.
What's gun lingers in your memory as kicking like a Missouri mule?