What I am wishing for is some kind of training grounds where you have static enemies to test the weapons on so you can find out the damage numbers and stuff like that. I feel like that could help massively in battles if you have that knowledge and could also be implemented / mixed with a map exploring mode, where you could choose your training ground to be any map or something like that.
If this doesn't make it, another similar suggestion would be to show damage numbers when choosing your gun, e.g. if you hover over a gun with your mouse a little window shows up telling you the headshot, bodyshot and anti-armour damage of this gun, or if you select the gun you get a little window somewhere in the menu, similar to big fps games.