Does shooting position affect Zero?

[TehLlama]

1. This is the AR Technical Discussion, so I don't see how the zero trajectory of a different weapon system, like a bolt gun with low sights, is relevant to the discussion.

We are talking about the zero of a rifle, which we all agree is when you do not need to make any adjustments to have POA/POI at a given distance.

While it is the AR Tech Discussion, bore offset is relevant, since that actually varies even within optic solutions for the AR platform (everything from absolute co-witness setups to carry handle mounted optics solutions), which can actually affect that a fair bit - add into the equation some of the unique pistol setups that can have a really low sight-over-bore and it's potentially germane to the discussion.

For my part, I consider the Zero to be something that takes into account a bit more - POA = POI @ a given distance for a particular load, at a specified altitude assuming flat muzzle-to-target and presence of muzzle device/can on the rifle... all things that can be changed with the rifle that ideally would mean acquiring a new zero. Anything beyond that is determining a dope based on windage, distance changes, elevation change, density altitude/barometric pressure, temperature (atmospheric, barrel/ammunition), and at the extreme end bullet precession, Coriolis, and transonic properties of the projectile.
Dope I consider to be anything that ends up being accounted for by turret adjustments FROM a zero, or a holdover (especially with a BDC reticle that runs windage ticks as well in the 1-2MOA precision realm), but I do want the zero to take into account as much as possible of the weapon configuration, and if significant altitude change is relevant (I live at 5980ft, so going to sea level moves stuff a bit @ 200m) I'd like to re-zero if possible.

Basically, I'd like to be able to return to a zero, and in the same or comparable conditions still be on point. Since a closer practical range zero is really ideal, then that can be really a consistent deal for a specific carbine w/ specific load, and being able to return to that zero (un-doping it) would be all I care about.

We do not physically adjust the bore axis of the barrel, by taking a tool to it and bending it up or down. The bore axis angle is elevated or depressed according to our sight adjustments.

Any part of my explanation that sounded off (especially what both you and F2S are consistently correctly stating that the trajectory is effectively static) is part of how I framed my answer, and how I tend to think about making sighting adjustments to the rifle - namely I work first from the assumption that my POA is actually at the dead center of where I'm aiming (not a great practical assumption, but requisite for this discussion), and that my POA sight line is actually on the target which is that set distance away, and make adjustments or assumptions from there.
For me, this means when I'm setting irons or something, the process I'm picturing in my head actually is moving the rifle (and hence trajectory vector at the muzzle) around in space from the fixed point of my POA line in space. It's a bit odd to think of it, but this lines up with the sight adjustment markings (basically if I need to move the POI center to the right, just crank in the direction of R marked on the sights/optic), and for my part makes it a bit simpler to think of BZO intersection points, and even making dope adjustments (basically picturing that if you have your POA lined up you're making optic/sight adjustments that ARE moving the barrel underneath your 'static' sights so that the bullet leaves, follows the trajectory, and intersects with that POA line somewhere in space as close as possible to the desired POI distance (and therefore hopefully dead center hits on target).

I can try to explain further, but that really is how I view it - everything in relation to a sight line that is considered to be imaginarily static, and the trajectory we're modeling as we start adding environmental factors starts to more closely bring the POI to the POA. This also helps when thinking of the weapon system itself deforming and moving - the only thing we can try to hold static in the model is that the sights are on target (or fliers can be usefully called) as the hammer starts traveling forward - this means that during the lock time and ignition delays, as well as elastic deformation of the barrel and other components in addition to extra forces imparted on the bullet as it goes from internal and transitions to external ballistics are all factors that get taken into account - since shooting position can affect these in different ways, that's part of the zero to me (for the chosen base position), and any alternate positions are then adjusted for using either a revised zero or a deliberate hold/optic adjustment to bring the POI back to POA.

For my uses, my sitting is really close across a lot of things - it lines up very close to my bipod prone as well as kneeling across the board, is only a touch (1.5MOA or so) above my magazine supported prone and tension slung unsupported prone, and is about 2MOA left and a tiny amount below for standing. This also works well since a disproportionate amount of easy points for the Table 1 USMC qual is about making hits in the sitting - prone at 300 is easy and the 500 is about making sensible wind calls and making the correct adjustments. Adding body armor it ends up being pretty close across the board - I got a bunch of stupid looks resetting BZO at our patrol base when I was sitting, but the shittalking from the grunts about some dumbass pogue doing it wrong went away when I made a single hole at 36yd with the last 7 rounds after a single 3-shot sight-in group.

[SkipD]

This whole thread is getting silly. The definition of "zero" is really what's being bantered about here.

In my opinion, the commonly accepted definition of "zero" by shooters that I know is very simple - making the point of impact be the same as the point of aim at a particular weapon-to-target distance. The other technical ballyhoo in this thread really has no bearing on real-world shooting as far as I see it.

The thread should be closed as it appears that we will never get anywhere resolving the definition issue.

[opsoff1]

This whole thread is getting silly. The definition of "zero" is really what's being bantered about here.

In my opinion, the commonly accepted definition of "zero" by shooters that I know is very simple - making the point of impact be the same as the point of aim at a particular weapon-to-target distance. The other technical ballyhoo in this thread really has no bearing on real-world shooting as far as I see it.

The thread should be closed as it appears that we will never get anywhere resolving the definition issue.

AGREED

[Enoch]

Another question about zeroing. In the sticky on zeroing "Molon" gives a great description about how to adjust elevation of the rear sight for shorter zeros than 300m so that POA will equal POI because the standard A2 rear sight is set for a zero of 300m and greater.

My Colt has a flat top without a carry handle and even the manual that came with the rifle, only describes adjustments and settings of a rear sight with a carry handle. Is the flat top with a pop up rear sight still initially set up for a 300m zero?

I am probably going to setup for a 100m zero but I am not sure how to adapt the info in the sticky and in the manual to my setup.

[John_Burns]

This whole thread is getting silly. The definition of "zero" is really what's being bantered about here.

In my opinion, the commonly accepted definition of "zero" by shooters that I know is very simple - making the point of impact be the same as the point of aim at a particular weapon-to-target distance. The other technical ballyhoo in this thread really has no bearing on real-world shooting as far as I see it.

The thread should be closed as it appears that we will never get anywhere resolving the definition issue.

Cool. 20 something posts you are already a SUPER MOD.

I, for one, enjoy FS2, Artic1 and Dano all posting in a thread.

Maybe you should start a lube thread??

Thanks to everyone else for a little discussion. Posting well thought out responses takes time and it is appreciated from some.

[Failure2Stop]

The environment/altitude (Density Altitude in aviation speak) in which ones zeros, absolutely will matter. Some people are fond of 200m zero's. In days of old, mil-dots, many long gunners would use 400m zeros. To minimize DA effects on zero a 100m (or 100Y), across the majority of rifle calibers/projectiles, zero is much more ideal. A 100m zero is good across a very wide range of elevation/DA. The trajectory after 100m then need be looked at.

With regard to positional shooting.. prone, sitting, standing, one armed handstand while gargling helium... yes the recoil management, or lack of, affects the POI as compared to ones original zero. High rd count 7.62 semi shooters are painfully aware of this.

Regard in "wind zero" aka adjust at 600Y. In service rifle one is doing a mechanical adjust off their earlier zero. At 600Y spin drift will have to be accounted for.

Usually one chooses the most stable, prone, repeatable zero position. Match shooters who frequently shoot the exact same positions, at the exact same ranges & will learn what works at each. In the case of service rifle competitions.. shooting a 15lb gas gun in small caliber(AR15), mitigates a lot of the POI variation aligned with the different positions differing recoil management/POI shift

This should stand as the final word on this thread.
Anything that follows this has better be of extremely high technical quality.