If you equate powerful = painful the most powerful hand gun was a 14" TC in 44 mag. I was stupid and fired 2 rounds of my own ammo. I guess the first one didn't hurt enough. The same ammo in my Ruger Redhawk 7-1/2" was comfortable.

In rifle it is my Sharps Quigley replica in 45-70. Loaded with Accurate Arms 5744 powder it was robust, switched to AA2015 and redefined agony -- good news it was only 5 rounds.

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S&WHF 366