When a zero is not really a zero

[VarmLR]

I'm a little surprised that this has gone on as long as it has on a precision shooting forum and is beginning to become a circular argument about "military" or "non-military" ways of zeroing!

 

The military definition is exactly the same as the non-military definition. A zero is only accurate at two specific ranges for each primary zero range chosen, and despite the arguments, can only be where POI intersects POA, the point of "zero" deviation from aim point to POI, because it defines a precise datum for making firing solutions for other ranges accounting for environmental conditions. You can "set the sights" however you like for any given POI but that is not the definition of a zero, juts a way of setting the sights.

 

http://www.wikihow.com/Zero-a-Rifle

 

"Zero" = "zero deviation from POA to POI"

 

http://battlefield.wikia.com/wiki/Zeroing

 

http://www.dictionary.com/browse/zero--in

 

 

Take your pick, they (and loads more definitions) all mean the same thing.

 

Setting for high impact at a given distance is not a zero. It's an MRT aim point or MBPR aim point. There's still a zero range for those aim points but it is beyond the range of the actual aim point for the sight setting for your chosen MRT.

 

We can split hairs until the cows come home, but whatever way you like to use your sights (ie whatever portion of the sight that you use for zero aim), POI must = POA at a given distance.

 

If we cannot agree on this, then we're all being pedants!

[Dalua]

Setting for high impact at a given distance is not a zero. It's an MRT aim point or MBPR aim point. There's still a zero range for those aim points but it is beyond the range of the actual aim point for the sight setting for your chosen MRT.

 

We can split hairs until the cows come home, but whatever way you like to use your sights (ie whatever portion of the sight that you use for zero aim), POI must = POA at a given distance.

 

If we cannot agree on this, then we're all being pedants!

So effectively, setting sights at, say 1.75inches high at 100yds is a zero. It's just that a lot of folks who zero like that (including me) know what that range is only rather vaguely - within the limits of the MPBR concept. I know the maximum point-blank range resulting from that setting, and I know that beyond that I must hold high. So maybe my 'zero' (meaning the range I can shoot with 'zero elevation') is the MPBR?

 

Does that make the description of a sight setting as '1.75inches high at 100yds' invalid as a description means of describing the 'zero setting' of that rifle and sight?

 

I think not: and I usually a tremendous pedant.

[gbal]

Bradders, here is some (more) data specifically on the effect of three degrees of cant on POA/POI at 600y:

 

243w105Berger Hybrid @300fps -a pretty flat shooting combo and 308w 175SMK@2600fps

 

243w Horizontal error 4.7",vertical error -0.1"

308w.Horizontal error 6.7', vertical error-0.2"

 

The more the drop/need for vertical click up compensation at distance,the greater the vertical cant effect.

Three degrees of cant is about what normal unaided eye can resolve (ie where there are no straight lines-mountains,desert etc).

It should do much better with a 'carpentered world' around-right angled refrence objects-buildings,target frames And the like.

Hope the eyes get reading again-I'll treasure the non literate,mute shaking shoulders image every time I hear about someone missing,and wondering why... Atb

 

g

[VarmLR]

So effectively, setting sights at, say 1.75inches high at 100yds is a zero. It's just that a lot of folks who zero like that (including me) know what that range is only rather vaguely - within the limits of the MPBR concept. I know the maximum point-blank range resulting from that setting, and I know that beyond that I must hold high. So maybe my 'zero' (meaning the range I can shoot with 'zero elevation') is the MPBR?

 

Does that make the description of a sight setting as '1.75inches high at 100yds' invalid as a description means of describing the 'zero setting' of that rifle and sight?

 

I think not: and I usually a tremendous pedant.

 

No, setting the sights so that POI is 1.75 inches high is not a zero. It's more like a mid range trajectory (MRT) setting. MBPR is a sight setting where the MRT at a set distance allows for the maximum spread of range where the MRT will still be within the kill zone of the animal that you are hunting at those prescribed (or worked out) ranges. It is not a zero except where the trajectory of the bullet intersects with the line of sight (aim point) which lies at two positions on the trajectory curve.

 

To most of us, that does mean that striking high for an aim point at your chosen "zero range" is not a true zero. As above, it's a sight setting for mid range trajectory where the arc of the bullet is on a high point compared with the point of aim. You could argue (and some have) that it is a zero because you know where your impact is at 100 yards, so can work a firing solution for any given range from there. True, but to me, it's still not a zero. Yes, you can work a firing solution from 1, 2, 3 or whatever inches high at 100 yards for any given range. The crux though is this: by definition, "zero" means "zero deviation" from point of aim to point of impact as already explained. Pedantry perhaps. I know that some want to argue the point to kingdom come (ok...I have been guilty too!), but perhaps best just to agree that one is a sight setting for a prescribed range where the other is a true zero at that range.

 

This is likely to just end up as "lets just agree that it means whatever you want to" because obviously the simple concept of zero deviation between POI/POA is lost in translation, or simply argued differently. If your version is valid to you, that's fine. I'm sticking to the more widely accepted definition but either way, it won't change my life

[gbal]

tackb-thank you for your generous comment in *66.

You are brief but correct in *68 -as Dalua elaborates,the ballistic calculator 'knows' what '1.5high at 100y' means as a zero,given the other info fed in carridge,bullet,mv etc).An experienced shooter often has a good practical knowledge for his rifle,so well done with your competition success,and don't sell yourself short.

 

You also say that -for you-it's imposssible to understand my post(s).I accept they are long. Some concepts get complex-I recall when I started in education,an old academic putting it thus- getting concpts across should help you understand better-both the concept,and your students. It should also help relieve tension,and give a sense of functional achievement,much like a cow giving milk.(nice image..very grounded!)

So it's a two-way thing...I'd appreciate it if you could PM me,saying which sentence(s)in my posts need to be clearer-but I think you have 'zero' pretty well zero-ed.a And your simple old self's success ('functional achievements') back that up !

Atb

g

[Dalua]

 

No, setting the sights so that POI is 1.75 inches high is not a zero. It's more like a etc. etc. ect.

It is not a zero except where the trajectory of the bullet intersects with the line of sight (aim point) which lies at two positions on the trajectory curve.

 

What you seem to be saying is that setting the sights so that the POI is 1.75" high at 100yds is not a zero, except for at the two places where it is a zero.

 

If that's right, then I think we might be agreeing that it actually is a zero. Or even two zeros Which is good!

 

I think that in common parlance, to 'set the sights' and 'to zero' are pretty much synonyous. I suggest some possible understandings of the word 'zero':

 

The actual act of zeroing sights i.e. the act of setting the reference-scale on the sight so that it reads 'zero'

 

The setting of sights so that the rifle can be used with zero elevation at the longest practicable range

i.e. my .270 set 1.75" high at 100yds has a zero range of 220yds when hind-stalking Ths results from my concept of the poi being acceptable if is is within 2" above and 2" below the poa.

 

Adjusting the sight so that the bullet goes to POA at a particular range. A useful concept if what you're shooting is the same size as the bullet-diameter, or smaller; always the same distance away; and your rifle and you can manage unwavering bullet-on-bullet accuracy at that range under all conditions. A narrow, unhelpful concept, of zero utility.

I'm finding not being a pedant for a change is quite liberating!

[Breacher]

The problem here is that setting up a rifle for point blank range and setting up a rifle for precision shooting is very different.

 

In the former, you measure the target you will be shooting at ( for example maybe a 4" circle if shooting deer ) and you set your sights so that it will hit SOMEWHERE inside that circle whether you shoot at your shortest or longest point blank range or any range in between.

 

In the latter you set your sights to hit the centre at a PARTICULAR range.

 

Whilst the former might work well and negates to some degree, the need to know range to target, to get a round SOMEWHERE within your chosen target - I prefer the latter as in my book, when shooting a rifle, I want the round hitting the CENTRE of the target or as near as I can !

[bradders]

[MrCetrizine]

[treetop]

I'm lost ,

 

So, is a zero a zero ? Or does it have zero effect if you zero your zero, on the zero ?

[Dalua]

I'm lost ,

 

So, is a zero a zero ? Or does it have zero effect if you zero your zero, on the zero ?

Yes.

[tackb]

What you seem to be saying is that setting the sights so that the POI is 1.75" high at 100yds is not a zero, except for at the two places where it is a zero.

 

If that's right, then I think we might be agreeing that it actually is a zero. Or even two zeros Which is good!

 

I think that in common parlance, to 'set the sights' and 'to zero' are pretty much synonyous. I suggest some possible understandings of the word 'zero':

 

The actual act of zeroing sights i.e. the act of setting the reference-scale on the sight so that it reads 'zero'

 

The setting of sights so that the rifle can be used with zero elevation at the longest practicable range

i.e. my .270 set 1.75" high at 100yds has a zero range of 220yds when hind-stalking Ths results from my concept of the poi being acceptable if is is within 2" above and 2" below the poa.

 

Adjusting the sight so that the bullet goes to POA at a particular range. A useful concept if what you're shooting is the same size as the bullet-diameter, or smaller; always the same distance away; and your rifle and you can manage unwavering bullet-on-bullet accuracy at that range under all conditions. A narrow, unhelpful concept, of zero utility.

I'm finding not being a pedant for a change is quite liberating!

 

you seem to be referring to MPBR which only works when you zero you weapon at a particular range and it requires you to settle for hitting somewhere around an aimpoint.

[maximus otter]

 

maximus otter

[tackb]

[Dalua]

 

you seem to be referring to MPBR which only works when you zero you weapon at a particular range and it requires you to settle for hitting somewhere around an aimpoint.

That's certainly what the second of the three things I've suggested as a 'zero' describes.

 

However, in truth I think most of us have to settle for 'hitting somewhere around an aimpoint'. We can either accept that truth, or pretend that, as I described in the third definition, that we can unerringly put bullet on bullet every time.

 

One could argue that there is a big difference between accepting a deviation of 0.25" from POA and accepting one of 4" - but both are useful in different roles, and both require the acceptance of a deviation from POA.

[Breacher]

Well folks - its time to end this thread I think.

 

We have learnt that opinion is divided on the subject - Daloola believes that his method is a zero whilst others believe it is actually PBR being misnamed.

 

Mods - feel free to lock

[MJR]

Seems ridiculous that people can't differentiate between zeroing ?

 

Anyway locked as requested.