The only cartridge that I have ever fired before buying a gun chambered for it is the .22 Long Rifle. Everything else...380, 9mm, 38 Spl., 357 Mag, 40S&W, 44 Mag, 45ACP and 45 Colt, I bought the gun first, because I wanted guns all across the spectrum. I didn't worry about what it would "feel" like. I just figured that I'd get used to it, and I did.
Along the way, I would've liked to have been able to shoot a 38 Super, since I've heard a lot of good things about that cartridge through the years. Maybe, even a screamer like the 9x23.
The next step in my progression would be something in the nature of a 454 Casull. But, I'm at the point and age now where another new gun on that level would just be silliness and the expense would be foolish. So, I'm good.