Concept: Tactical shooter multiplayer deathmatch game. Your starting weapon is a Kolibri, the early C20 Austrian 'meme gun' known as the smallest automatic handgun ever made. Every time you score a kill, however, your gun scales up to a slightly more powerful cartridge. There's a brief period during which you have an actually practical gun. And then 10-ish kills in and you're shooting rifle cartridges out of a short-barreled blowback pistol, and the recoil and flash is so much that every time you shoot you are basically stunned for a second. If you die, you reset back to 2mm Kolibri.
The winner of the match is whoever scores a kill with the biggest cartridge, a 20mm cannon round fired out of a comically oversized gun. Of course, shooting this causes the gun to explode and takes you out too, so you only get one shot.
you start with a sharpened-flint spear and end with a 800mm railway gun. Everything takes a realistic time to load, aim and fire. Maps are several miles across. Sure you only have a flintlock musket, but if that howitzer misses maybe you can get in range and gun down the operator before they can reload.