For ELR what constitutes a good zero?

[Professor Doolittle]

It just occurred to me that the practice of taking a single shot to test the zero doesn't make any sense if you care about accuracy.

the way I was taught:

1. shoot a group at 100 yards
2. find the center of the group
3. zero the scope to this data
4. take a single shot to test the zero near bullseye

But that single shot at the end isn't an adequate test, it has to be another full group with the center now on the point of aim. A single bullet dead on the bullseye is misleading because every bullet is part of a statistical dispersion and that one bullet may not represent the group's center even though it looked great.

If you only care about a rough zero I guess that's fine but in my case I was trying to adjust Hornady's 4DOF axial form factor, but that feature is to address a difference of like a quarter inch in a 600 yard shot. If the zero is not perfect than axial form factor is just compensating for poor zero.

 

[Bravo 4]

Not being rude brother, but I think you are overthinking things. If #1-the rifle is capable of great precision (little groups) and #2- I feel I made an accurate shot, then I'm fine with checking zero with one shot. If either #1 or #2 are iffy, fire another shot or two (a group) to check. If I feel a shot wasn't right during zero or load data, I'll somewhat discard that shot and fire again. Or if I call it something like .2 mils left and it hits .2 left I'm fine with that.

 

[tobnpr]

^^^
This.
1/4" impact shift at 600 yards?
There's no substitute for sending a lot of lead downrange to practice your wind calls.
Ballistic solutions are amazing these days but that 1/4" you relate is dwarfed by real-world conditions that the computer cannot address.

 

[Jeff Heeg osoh]

So if your zero has been confirmed and reconfirmed at a 100 and lets say you are off the 1/4" at 600 how would you explain being a 1/4" off on your program at 600 or worse yet when you get to 800 now its more then 1/4" all this being done with the correct speed being entered in that also has been confirmed by a quality chrono. just asking what you would look at as the correction or cause, I know it sounds like a test but many over look this.

osoh

 

[257 STW]

I true and confirm my drops by adjusting the velocity in my Kestrel. No matter what your chrono and ballistic solver tell you, you should always check your drops and adjust velocity slightly to verify your POI at distance. I know some who adjust BC numbers for the same results. That is just how I do it for my drops out to 1300 yds, and is still on to a mile which is the farthest I have shot to date. my .02

 

[Professor Doolittle]

So if your zero has been confirmed and reconfirmed at a 100 and lets say you are off the 1/4" at 600 how would you explain being a 1/4" off on your program at 600 or worse yet when you get to 800 now its more then 1/4" all this being done with the correct speed being entered in that also has been confirmed by a quality chrono. just asking what you would look at as the correction or cause, I know it sounds like a test but many over look this.

osoh

Well in Hornady's 4DOF app they have a fine tuning adjustment called "axial form factor" for pulling in that last .25 inches. I think the max range of this fine tuning is like an inch, if you're off by more than that then the problem lies elsewhere.
Now if after that you then shoot a group at 800 yards and its off again but still correct at 600 yards then it could be a scope tracking error. That's assuming the app is correct, which is a good assumption.
The variation in muzzle velocity is the most important thing of all from the numbers. I have used Labradar with Berger bullets and a fantastic standard deviation for speed at 3100fps average is like 12fps. So plus or minus one std dev is 24fps which is the difference of a full click, .1mrads at 1000 yards. That means that the speed is all over the place over-washing a one click dialing error even with the best bullets. The probability chart is saying there's a 34.1% chance that the first bullet will be 12fps fast and a 34.1% chance the next bullet will be 12fps slow. So, that's where I would look first, that the velocity you input to the app is not exactly accurate.

 

[Professor Doolittle]

I true and confirm my drops by adjusting the velocity in my Kestrel. No matter what your chrono and ballistic solver tell you, you should always check your drops and adjust velocity slightly to verify your POI at distance. I know some who adjust BC numbers for the same results. That is just how I do it for my drops out to 1300 yds, and is still on to a mile which is the farthest I have shot to date. my .02

That's interesting. I just posted on this very idea a second ago but I never heard of someone truing their velocity input. That's a great idea.

 

[bigngreen]

Taking a 100 yard zero and actually having something good is difficult, I spend little time on the 100 yard zero because it's the worst range you'll shoot, not settled down, parallax issues all make that 100 yards zero change. I use 300 yards to confirm and dial in my 100 yard because at 300 the velocity or BC won't show up in a meaningful way but a 100 yard zero being of will show big so I basically zero at 300 and reverse the ballistics back to 100 yards and input the correction in app not even change my physical zero cause it's close enough for hunting. I then run it out to 1000+ yards single shot on paper as fast as I can all at the same time dialing so I'm as close to the same condition as possible. So after my zero is tuned it's one round at 300, 600 maybe 800 and then at 1000 and maybe 1500 in as fast a time as I can send it while shooting solid, this gets me dial the quickest, I may tune velocity a few feet per second by 1000 but I wouldn't be looking at form factor or BC till beyond a 1000 and even then it would be moderate if everything is right. By the time I'm tuning ballistics I'm well beyond group shooting, I'm in the mode that if the first round isn't on then a group isn't going to do anything but waste bullets.

 

[Professor Doolittle]

Not being rude brother, but I think you are overthinking things. If #1-the rifle is capable of great precision (little groups) and #2- I feel I made an accurate shot, then I'm fine with checking zero with one shot. If either #1 or #2 are iffy, fire another shot or two (a group) to check. If I feel a shot wasn't right during zero or load data, I'll somewhat discard that shot and fire again. Or if I call it something like .2 mils left and it hits .2 left I'm fine with that.

Lets say you have a two inch group and zero and take a single followup shot that hits dead on the bullseye. That single shot could be off the true group center by an inch even if there's no mistake in how the zero was adjusted. That's eight inches at 800 yards. That's error on top of all the other errors. Because of the fact that errors can be positive and negative and cancel each other out a person can be fooled by the result, so to my mind you have to nail down every source of error individually.

 

[Professor Doolittle]

Taking a 100 yard zero and actually having something good is difficult, I spend little time on the 100 yard zero because it's the worst range you'll shoot, not settled down, parallax issues all make that 100 yards zero change. I use 300 yards to confirm and dial in my 100 yard because at 300 the velocity or BC won't show up in a meaningful way but a 100 yard zero being of will show big so I basically zero at 300 and reverse the ballistics back to 100 yards and input the correction in app not even change my physical zero cause it's close enough for hunting. I then run it out to 1000+ yards single shot on paper as fast as I can all at the same time dialing so I'm as close to the same condition as possible. So after my zero is tuned it's one round at 300, 600 maybe 800 and then at 1000 and maybe 1500 in as fast a time as I can send it while shooting solid, this gets me dial the quickest, I may tune velocity a few feet per second by 1000 but I wouldn't be looking at form factor or BC till beyond a 1000 and even then it would be moderate if everything is right. By the time I'm tuning ballistics I'm well beyond group shooting, I'm in the mode that if the first round isn't on then a group isn't going to do anything but waste bullets.

Interesting. Why not just punch in the 300 yard zero into the app and let it go at that, then? Why back-reference it to 100 yards? Which app do you use? And you're right, its a big expense to chase precision by doing everything by groups, especially at $6 per bullet. I shoot .300 Norma mag.

 

[bigngreen]

Interesting. Why not just punch in the 300 yard zero into the app and let it go at that, then? Why back-reference it to 100 yards? Which app do you use? And you're right, its a big expense to chase precision by doing everything by groups, especially at $6 per bullet. I shoot .300 Norma mag.

Because the trued 100 yard zero isn't as influenced by big enviro or elevation swings so it's easy to check and use as a base.

By the time you shoot a group, drive down and measure it then tune things and then shoot to confirm your enviros have changed, for fast accurate results pick your time on your best condition and rally through it, I like to get large targets put out in the dark and have everything ready and set up and when I get that still morning air before the sun is up and screwing with me I hammer out the shooting.

 

[Bravo 4]

Lets say you have a two inch group and zero and take a single followup shot that hits dead on the bullseye. That single shot could be off the true group center by an inch even if there's no mistake in how the zero was adjusted. That's eight inches at 800 yards. That's error on top of all the other errors. Because of the fact that errors can be positive and negative and cancel each other out a person can be fooled by the result, so to my mind you have to nail down every source of error individually.

Why would you be shooting a rifle only capable of 2" groups at ELR distances? That's insanity!
That's why I said great precision.

 

[Bravo 4]

That's interesting. I just posted on this very idea a second ago but I never heard of someone truing their velocity input. That's a great idea.

When you true in a kestrel it adjusts the muzzle velocity. That is only going to get you so far, at some point the algorithm isn't going to match actual drops. Things like actual BC and actual scope turret adjustment is going to rear their ugly heads. We teach this, but for ELR you are going to run into problems.

 

[257 STW]

When you true in a kestrel it adjusts the muzzle velocity. That is only going to get you so far, at some point the algorithm isn't going to match actual drops. Things like actual BC and actual scope turret adjustment is going to rear their ugly heads. We teach this, but for ELR you are going to run into problems.

I completely agree. I think that`s true with any bullet. I shoot only Bergers, and it seems to me that the BCs are fairly accurate as per Bergers numbers. Scope mechanics, and tracking are another story, as scope quality goes up so does turret precision IMHO. Wind is our biggest adversary at distance. I do use a 100 yd zero, but do not start shooting groups till 500, just to verify my loads are consistent, and group well (usually 1/2 moa or better) While I do shoot steel at a mile for fun, most of my practice is from 500 to 1300 yds as that is my self imposed max for hunting depending on the game. my .02