The 40mm might kick a bit too much. Last one I saw was mounted on a ship.
Now, the .40 cal is a bit different.
I once owned a Springfield Armory XD 40. To be honest I couldn't hit squat with it. I traded in on a 1911. The .45 acp is my favorite caliber for both accuracy AND effectiveness. I recently bought my first 9mm and I gotta tell you I'm impressed. I don't think a person is undergunned one bit with a 9mm either.
Of course the .40 cal is extremely popular these days, largely due to so many law enbforcemet agencies, like the FBI switching to them. The only advantage I can see in the .40 is a bit longer range than the .45.
The bottom line for me is it would seem the .40 wss designed to fill a gap that wasn't there. Actually it was the result of FBI complaints about the recoil of the 10mm effecting the speed of follow up shots. If iI felt I needed a more potent round than the 9mm, .357 mag, or .45, the 10 would be my choice.
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