"Every weapon" >>>> Rifles and above caliber 1 shotting to the head, chest and stomach
If you read the reply chain AMURKA quoted a post of mine:
When all the (rifles and above calibers) can kill in 1 shot (to the head, chest and stomach), damage doesn't even become a factor in weapon balance and this increases weapon variety because people will choose a gun that suits their playstyle rather than the highest damaging gun such as the G3 and FAL.
Example: If you want to do long range shots you should pick a gun with high velocity, low recoil (ideally the m16/SKS)
Example: If you want to play up close you should pick a gun that has a high rate of fire, large magazine size, light weight and a fast reload (a full auto AR)
^to go even further, a submachinegun like the mp5/mp7 is even better with all those points - but it is then balanced to not kill in 1 shot.
Example: if you want to be a specialist and clear people through wall on the objective you should pick a gun that is a larger caliber and has increased penetration (a 7.62 gun)
I can assure you that the G3 does 2 of those and even more! - it can kill with 1 bullet to the chest+stomach where the other guns can't. When picking a weapon, damage is the most important weapon property and people will naturally choose the highest damaging gun. When the rifles and above calibers can kill in 1 shot to the head, chest and stomach, damage isn't important and people will then choose a gun that matches their playstyle instead of a catch-all OP 1 shot weapon. This increases weapon variety.
Not being able to 1 shot to the head, chest and stomach means the game becomes full auto spraying gameplay rather than properly aiming, tracking and taking your shots.
This is because you cannot kill in 1 shot so you need to fire as much as you can to increase your chances that 2-3 of you bullets will connect. This means it becomes a game of DPS and recoil control to drag your mouse downwards as you fight the vertical recoil of your gun. This is mindless and unfun gameplay with little depth. Even with only the head killing in 1 shot, you would still be doing the full auto spraying towards the head - you would not be taking your shots. Taking shots = depth to the game.
This is in a 1v1 facing each other obviously. If you sneak up behind someone then you can use single fire to the head.
Killing in 1 shot and being killed in 1 shot means you actually have to put thought into your movement instead of sprinting around everywhere - being reckless will get you punished and killed since you won't survive the first bullet. Right now in Sandstorm's current state you can often run and out in the open, tank bullets (even from a sniper) and keep running.