A .22 shouldn't have the same stopping power as a shotgun. This might sound obvious, but two .22 rounds to the chest shouldn't be knocking a zombie on their ass the same way a shotgun to shell to the chest should. Two or three .22 rounds to the chest shouldn't even phase them. They shouldn't even notice being shot by them. I think different ammo types need to have unique interactions with the zombies. .22 shouldn't phase them. 9mm and .357 should slow them down a bit once you pump a few rounds into them. 6.8, 5.56 and maybe .308 should stop them in their tracks. And shotgun shells are the only thing that should knock a zombie back on their ass after a single shot. This would not only make more sense, but it would make the different gun types feel unique.
When I say weapon damage should be adjusted, I think on the higher difficulties headshots should be far more important. You can kill zombies in this game with just a few 9mm rounds to center mass. That shouldn't be anywhere near enough. Again, the only ammo type that should have a chance of killing a zombie with chest shots are shotguns since the sheer power might damage the spine enough to where they can't walk. Zombie body health should be significantly increased so players can't easily score kills by shooting the body. It would be really cool to see zombies missing arms, their chest open, but still walking around because their head is intact.
Lastly are the ammo type weights. 20 rounds of .22 shouldn't weigh anywhere NEAR as much as 20 rounds of 12 gauge. Not only does it not make any sense, but it mostly defeats the purpose of having light and heavy ammo types in the game. Why carry a .22 when you can have a shotgun which is objectively better? Instead, the smaller the ammo type, the lighter the ammo should be. That way carrying a .22 handgun, while not as powerful as a shotgun, allows you to carry far more shots. Having all ammo weight roughly the same removes a layer of strategy from the game.
