There are a lot of things which can cause a jam. Ammo could be bad (poorly sized, shape of nose, underpowered, overpowered), cleanliness of firearm (last cleaned when Grandma Moses was learning the alphabet), condition of firearm (worn or broken parts), bad magazine (lips bent, dirt, deformed, follower spring weak) operator error (limp wrist), ad infinitum.
The challenge for the engineer is to develop a gun which tolerates the above and yet function reliably and accurately despite all these problems.
A challenging cartridges is the 40 S&W. Dang good bullet and it's taken LE & America by storm. But what a nightmare. It has the narrow base of the 9mm but tapers out to 10mm diameter. Unlike the .45 ACP, it is supersonic and higher pressure, so the case must be supported. You can't widen or flare the chamber mouth on a 40 S&W like you can for the .45 ACP. The follower also has to compensate for the odd shape of the cartridge. A worse bullet to design a semi-automatic pistol for is the .22 Short. Stubby little sucker with a rim.
Yep, engineers worldwide adapted designs to all sort of calibers and I give a lot of credit to those guys. But they can't anticipate every new bullet design for a particular caliber and guarantee that their gun will work. Most of the time it does, but sometimes it doesn't. Nor can they control the secret super load being developed by a reloader out there.
That said, the user is responsible for finding find out what works reliably and accurately with his/her particular firearm...and stick to that combination whether engaged in competition or (hostile) conflict resolution.
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