Is Zero on a scope shooter specific?

[JimStC]

Been thinking about this lately. My wife and I shoot bolt action and semi auto rifles on a 160 yard range in the back part of our property. We shoot from bags and when dialing in a scope from a Caldwell sled.
Calibers are 17 HMR, .223 and .204 Ruger. I install and zero my scopes and have done so for years. Scope models are NightForce, Swarovski and Leupold.
I have been noticing that when I am shooting very good groups and then we trade rifles that I do need to make some elevation and windage adjustments for her.
I have thought about trigger pull as a potential culprit but is it also our differing eyesight, cheek position, shoulder placement of the buttstock and so on?
Will appreciate some thoughts on this,
Jim

 

[rcmodel]

Yes, it will be different.
Not a lot, but different.

Reasons probably have more to do with the way the rifle is held, IE: how solid against the shoulder, the weight of the mass the shoulder is attached to, how much it can start to recoil before the bullet gets gone, etc.

rc

 

[T Bran]

I recently got a friends wife to start hunting with us ( she's now addicted ). To lessen recoil I built some reduced loads for my old 760 in 30/06. I took the rifle to the range at the club and got it zeroed from a vice. When she had time we took it to the range again for her to do some practice shooting. The scope needed no adjustment even though she's left eye dominant and shooting lefty. This really shocked me since she is right handed I at least expected to do some fine tuning.
While not a perfect sampling it does lead me to beleive that once sighted in they are good to go.
For someone who has no rifle experience she is an amazing shot some folks are just naturally inclined. Cant wait to get her on some hogs but they were a bit leery last weekend only showing up after dark.
T

 

[JimStC]

Thanks for the responses.
RC, your comments are what I suspected particularly with regard to the shoulder hold relative to recoil prior to launching the projectile. Like you said it is 1-3 1/8" clicks. Not a lot but enough to wonder about the dynamics at work.
T, you are a good man to get a woman shooting and hunting. The more the better to me. My wife and I shoot 5-6 afternoons per week. She is ready to shoot whenever. I am a lucky man.

 

[trex1310]

I agree with RCMODEL. I think the way the shooter holds the rifle
is the biggest culprit. Second would be trigger pull.

 

[1hobie]

Parallax error is probably the main culprit. Yes, different shooters on the same gun will experience this as will a shooter that doesn't maintain exactly the cheek weld/hold.

http://en.wikipedia.org/wiki/Parallax

Hobie

 

[JimStC]

Hobie,
Good article. Thanks,
Jim

 

[beatledog7]

Not just shooter-specific. Something as simple as the difference between wearing a t-shirt and wearing a heavy field jacket can make a significant difference.

Anything that changes the relative positions of your eye and your optics matters to some degree.

 

[taliv]

And yet when I took two young new shooters out a couple days ago, they both made first round hits on a tiny target at 685 yds with the same rifle.

On a properly set up rifle I think the Difference if any is trivial for practical shooting.

 

[JimStC]

Taliv,
Hitting a target and shooting sub .3 MOA are two entirely different endeavors.
My rifles are set up properly. We are a 5'10" 200 lb man and a 5'4" 120 lb woman. Both of us hold our rifles differently and have very different eyesight.
Recoil sensitivity to her and hence the anticipation of such is drastically different from my sense of recoil. (excluding the .17 HMR of course)
I'd also recommend that you read the above referenced article on parallax error before you call into question my ability to set up a rifle. Also consider the other insights shared above.

 

[taliv]

they're not really that different.

but is it also our differing eyesight, cheek position, shoulder placement of the buttstock and so on

and then we trade rifles that I do need to make some elevation and windage adjustments for her.

My rifles are set up properly. We are a 5'10" 200 lb man and a 5'4" 120 lb woman. Both of us hold our rifles differently and have very different eyesight.

set up properly for whom?

i understand parallax error, but i assumed if you're that picky about shooting, you'd have a scope with adjustable parallax (i know the 3 brands you mentioned offer that feature) and the two of you would focus it each time you got behind the rifle, along with the diopter.

are you saying you're not changing the parallax when you give her the gun?

 

[JimStC]

"they're not really that different." Really?? Thank you for your opinion. Anecdotal comments are much appreciated.

The parallax adjustment on our scopes is not a direct adjustment. It is done via the adjustable objective. These are older scopes.

Of course we adjust the diopter, every time we swap rifles to optimize clarity

"Set up properly for whom?" Set up and installed properly in a generic sense with the adjustments made as mentioned above for each shooter, hence the reason for my first posting question.

 

[matrem]

On a properly set up rifle I think the Difference if any is trivial for practical shooting.

This has been my experience as well.
I've seen numerous rifles shoot to within moa or less with multiple shooters (and no adjustment).

 

[taliv]

yeah, really. what is so different about them. you're still just trying to put a bullet where you want.

so if you're adjusting the parallax already, then that's not your problem.

moving your head around on the stock only changes the POI if your parallax isn't properly adjusted. holding the stock in different positions won't change the POI. if it did, the practical matches we shoot would be impossible because almost all our shooting is from barricades, positional, etc. almost no bench shooting.

maybe if the rifle isn't bedded or the barrel free floated or something, that would change it. that's a possibility given the smaller calibers you mentioned. is she positioning the bags touching the barrel?

 

[JimStC]

Ok, one last try although I am not sure why I am wasting my time.

In this thread there are a number of valid reasons for the changes. Evidently, Taliv is dismissing them all. His/her premise is that practical shooting at targets on the run, behind barricades, etc is the same as shooting from bags with the objective of hitting the same bullet hole multiple times.

Therein lies the error. I have competed for years in Multi Gun and when I am sending a shot down range. I have one objective: hit the A zone, period.
The A zone on a USPSA target is 6" wide and 11" tall. There is no way I can measure with any precision or accuracy if my shot went exactly where I wanted it to go. The fact that I am engaging multiple targets makes it even more difficult to determine point of aim versus point of impact for each shot. Obviously some stages will limit the shot placement on the target to a smaller area but never to the size of a .2xx bullet hole.

Thanks to everyone for their answers and insights.

 

[taliv]

Jim I don't know why you're getting offended here. I'm not talking about 3 gun. I'm talking about shooting at very small (typically 1moa) targets at ranges from 300-1200 yrds and it's not scored time plus so everyone is taking well aimed shots just from very nontraditional positions.

When I get back to my pc I will post some links to pics so you can see the types of positions involved where the competitors are still hitting moa targets without proper cheek welds and holding the stocks in all sorts of different ways.


Aside from that I've only seen one valid reason in this thread that would cause your wife to shoot to a different poi when the gun is on a bag or lead sled and that is parallax which you said you have been adjusting for that already so I don't think you're anywhere close to finding the culprit yet.

Btw adjustible objectives are actually better than side focus parallax they're just not as convenient.

 

[taliv]

Just to be clear I'm saying that when I shoot the bullet almost always goes where I had the gun pointed when I pull the trigger. If I miss from a barricade it is because I had a bad position and was wobbling around not because the barricade itself did something wacky to cause poi and poa to diverge.

Sure it might do that if you rest the barrel itself on the barricade or if your gun isn't bedded properly and you're putting some sort of crazy tension on the stock but that's not going to be the case in a lead sled or just shooting off bags from a bench.

In my experience shooting groups from a bench my shoulder placement doesn't change poi. It's important for riding the recoil on the bags and for fast follow up shots so you can shoot the group before the wind condition changes but just holding the stock tighter or looser and moving my support hand fore or aft do not change poi for me.

 

[Double Naught Spy]

Will appreciate some thoughts on this,

I regularly shoot with two guys and between the three of us, we have quite a variety of gear and we often shoot one another's guns for various reasons, especially on days when one of us is trying to sight in a gun and is having problems for some reason. At that point, it is good to rule out whether it is a mechanical/optic issue or a operator issue.

This what I find strange. The zero on my rifle at 100 yards is usually about 2-2.5" inches off for Shooker K and the same on his rifles for me. The zero for Shooter J and me is generally less than an inch and usually more like half an inch. His guns are sighted in left handed, BTW. The difference between Shooter K and Shooter J is more like 3+".

So we don't worry too much about each other's zero point. If I am having trouble getting good groups with some new ammo or a new scope, I might get Shooter K to put 4 or 5 rounds down range to see how he does. If he shoots a tight little group 2" out at 7 o'clock from his POA, then the issue is me. If he can't get a good group, then we work to rule out other issues.

 

[taliv]

Double naught what do you think causes that?

 

[JimStC]

Taliv,
Please post the pics and if there is a web site describing the type of competiton you are mentioning, give me a link to that too. Sounds like fun.

DNS is pointing out the same problem but with much greater variances. I am talking about three .125" clicks on our variance. What would cause that?

 

[taliv]

Will post some this evening. I'm in an airport at the moment.

I'd really like to know too. It's an interesting topic and I'd like to poke at it until we get a reasonable theory or two. Again parallax is the obvious culprit as suggested initially but for the sake of argument I'm assuming you've adjusted that out properly. I wonder if the scope isnt working.

Actually let's do a test. Mount the gun in the lead sled. Aim in at the target. Adjust the parallax until you can move your head left right up down and the crosshairs stay on target. Now without touching the knobs get your wife to do same and see if it is still on target for her

 

[BADUNAME37]

One thing that comes to mind is, if the rifle is not perfectly plumb (vertical with the scope's crosshairs vertical and well-aligned), that will make some difference in POI. I realize it is not much, however, the further you shoot, the more error it will be! Also, the height of the scope from the center of the bore plays into this equation.

I know I like my scopes set up perfectly in line with the rifle when the rifle is essentially perfectly straight (level, plumb, etc).

When I look through some people's scope-rifle setups, I am amazed that some people can have the scope canted as much as several degrees (out of 360)! I wonder to myself, do they hold the rifle crooked so the scope hairs appear perfectly in-line or do they hold the rifle the way it "feels right" to them and that ends up being several degrees crooked with the crosshairs in-line!

Either way, it has to make a difference in POI at, say, 100 yards and greater!

 

[JimStC]

I was just out sighting in a scope I changed on my .204 semi. Just can't leave well enough alone.
My wife and I will go out in a few minutes and run that test. We'll use the Savage Model 12. Heck with the NF scope on it the weight is 13.5 lbs and there is little chance for operator error on that rifle. Sled is already out sitting on my shooting table.
I will report back.....

 

[Jenrick]

Assuming a laboratory shooting environment of STP with no wind, an ammo lot of 0 SD in velocity and pressure, and a barrel that does not wear (so a whole lot of theoretical stuff) there should be precisely one "zero" for a given optic and weapon. The true optical center of the lens (assuming it perfectly matches the center of a given reticle), after adjustment coincide with the bullet impact at a given range generating a POA/POI "zero."

Assuming that the human eyeball used to "zero" the weapon is placed directly in the center of the optical path, any other eyeball that is placed in the center of the optical path will have the same bullet strike as the original. However if the original eyeball was not centered in the optical path, then it's just a guessing game where the bullet strike will be for any following shooter who may or may not be centered in the optical path. Now the degree of error of the original eyeball, and any following shooters can range from minuscule (well below the capabilities of the rifle, ammo, and shooter) to excessive (very noticeable shift in "zero's").

The best way to ensure a usable zero for most shooters is to exercise good fundamentals in terms of stock placement, eye relief, etc. and ensure follow on shooters do the same.

 

[JimStC]

Jenrick,
Wow, you very succinctly enumerated the multiple variables. Thanks for the input. Now if I can just get my wife out of her garden (about 3 acres) we can go run some tests.
I do sincerely appreciate everyone's comments on this thread.
Thank you and please keep the personal experiences and observations coming.

Taliv: I found the web site. That is some cool stuff. Do they let old men play?