I don’t know who came up with this, or why so many officers and NCOs seem to think it’s gospel, but this is a concept that has to go away.
The idea of the “combat BZO,” and I’ll get into BZO (battle-sight zero) in a minute, is that in order to have your weapon properly zeroed for combat, you have to zero it while wearing all your kit, because somehow the kit on your chest and head changes the impact of the round.
Anyone with the slightest grasp of basic mechanics should see in a matter of moments how wrong this is. The zero is a mechanical relationship between the alignment of the sights and the barrel. Nothing more, nothing less. If your weapon is properly zeroed, then correct sight alignment, sight picture, breathing, and trigger control will cause the round to impact where it is aimed. That is all. If you are off because you’re wearing your kit, it has nothing to do with your gear, it just means that your gear isn’t set up correctly for you to get proper sight alignment, in which case you need to fix your kit. The whole concept of “battle-sight zero” being somehow different from a strict zero is equally flawed. A zero is a zero. Either the sights are properly calibrated to the track of the bullet, or they aren’t.
The only thing trying to zero in armor, ammo, water, and helmet ultimately does, is create enough discomfort that it becomes more difficult to group well enough for a solid zero. The end result often turns out to be a “good enough” zero, which might be in the ballpark, but isn’t really on.
Unfortunately, what should take only a few moments of thought and common sense seems to elude a lot of people, and often those with the rank and experience that they should know better. I’m not sure where it comes from, though I suspect it has something to do with following procedures rather than really getting to know your tools.
A carpenter knows his tools. An electrician knows his tools. A shooter should know his tools at least as well, certainly understanding how they function at a level higher than “pull the trigger and it goes bang.” Simple, easy-to-acquire knowledge, not to mention a handful of seconds to think, would make this disappear, and get back a lot of wasted time and ammunition.