when to call a rifle "zero'd"

[z7]

thanks for the valuable input. to help explain just a little, it is a target rifle, I plan to shoot 100 to 1000 yds. Manatee gun club near sarasota has steel at 600 and 1000 and when I go I can set up on a bench and alternate between the two. I can also set a paper target anywhere from 100 to 1000.

center of the group is currently a hair low and maybe 1/4" right or left depending on my windage. I need to reset my windage turret to zero, but how much do you all tweak your target rifles. I have 200 rds of that load (175smk, win brass, cci 200 and 45g varget-MAX LOAD, don't copy without doing your own workup) and I will retest before going on to distance. a small elevation issue will not cause much of a problem as I do not have a chrono, so my dope for elevation at 1000yds is going to be trial and error. I assume around 2700fps, now I gotta shoot it.

for windage though, a little right/left offset I am afraid could hamper my ability to learn how to read the wind by giving me a false indication when shooting for a 5" plate at 600yds.

would YOU tweak the windage a little using the ability on my scope to try and go "in between" the .1 mil clicks to line my windage up a little better.
I will be verifying at the range from the same bench type position I will be shooting at long range with. my hesitation is that I am not really familiar with that adjustment and I could end up overdoing it, requiring a few adjustments and headache when what I have is more accurate than I have ever been able to achieve.

I know it can be better, but for me this is remarkable. maybe i'll just stop worrying and shoot more

 

[LoonWulf]

maybe i'll just stop worrying and shoot more

Id probably go with THAT.
I would also suggest going ahead and getting a chrono, guestimating velocity can be spotty at best. For instance my load for my 6.5creedmore is book suggested at 3k+ from a 24" tube, from my guns 22" im only getting 2850. Now If I use any of the ballistics programs, id figgured an 60-80fps loss from the 2" shorter barrel, getting nearly double that will throw my calculations out considerably.

 

[horsey300]

thanks for the valuable input. to help explain just a little, it is a target rifle, I plan to shoot 100 to 1000 yds. Manatee gun club near sarasota has steel at 600 and 1000 and when I go I can set up on a bench and alternate between the two. I can also set a paper target anywhere from 100 to 1000.

center of the group is currently a hair low and maybe 1/4" right or left depending on my windage. I need to reset my windage turret to zero, but how much do you all tweak your target rifles. I have 200 rds of that load (175smk, win brass, cci 200 and 45g varget-MAX LOAD, don't copy without doing your own workup) and I will retest before going on to distance. a small elevation issue will not cause much of a problem as I do not have a chrono, so my dope for elevation at 1000yds is going to be trial and error. I assume around 2700fps, now I gotta shoot it.

for windage though, a little right/left offset I am afraid could hamper my ability to learn how to read the wind by giving me a false indication when shooting for a 5" plate at 600yds.

would YOU tweak the windage a little using the ability on my scope to try and go "in between" the .1 mil clicks to line my windage up a little better.
I will be verifying at the range from the same bench type position I will be shooting at long range with. my hesitation is that I am not really familiar with that adjustment and I could end up overdoing it, requiring a few adjustments and headache when what I have is more accurate than I have ever been able to achieve.

I know it can be better, but for me this is remarkable. maybe i'll just stop worrying and shoot more

Windage adjustable scope mounts.....Leopold if I remember right. Did the trick on my .300, they'll get ya straighter sooner, at 1000 yds, your .25" grew quite a bit, now factor in a bit of wind....you'll be less pleased, at 600? Less of an issue, not awesome, but not AS bad. The fact that you're asking about it already shows a lack of confidence in what's going on, and 30 idiots online can't repair that. First couple of misses or "good enough" hits will have you wondering a LOT more than you are right now. Your test groups don't have a lot of holes so in theory you MAY have a sub moa load, you MAY have a 1.25 moa load. That 5" plate you wanna ring at 600 is sub moa, your second group measured .7" right? Add .25" of doubt and a 5 mph breeze and you won't be sure if it's you, your load, your scope, or your gun. When I'm stretching distances, my targets are hit with cold dirty bores and I never doubt my scope nor my load, that means the rest of my focus is solely on ME and the target connecting. If something is wrong, it's my calculations or something fundamental (like too much coffee ). Hitting the center of where you wanna hit is the best start for confidence in the following shot, whether that takes place in 60 seconds or 6 days, it makes a difference. You reference setting up a bench, but didn't say if you had shot those groups from a bench, I shoot prone whenever possible, I zero prone. If you're shooting from a bench, zero from the bench. Good luck and enjoy! Either way it'll be time well spent!

 

[Llama Bob]

Windage adjustable scope mounts.....Leopold if I remember right.

I've mentioned this before, but I'll say it again. HE HAS A SCOPE THAT HAS SUB-CLICK ADJUSTMENT CAPABILITY. He does not need any shims or special rings or whatever. See page 12 of this manual:

http://www.vortexoptics.com/uploads/web_manual_rfl_razor-hd_gen2_ffp-13a.pdf

It's an screw with arbitrarily fine adjustment.

The question OP has is whether to use that capability here. To which the answer is "sure" as long as the POI vs. POA discrepancy is truly repeatable.

 

[Bart B.]

There's an old rule of thumb that circulates among top ranked competitive shooters. Never make a sight change smaller than 1/3rd the size of the group's you shoot. Otherwise, you'll probably not see any average point of impact change over the next few shots.

That's why Warner rear sights used on Palma match rifles have 1/2 MOA clicks for use at 800 to 1000 yards even though ammo tested in them shoots near 1/2 MOA at those ranges. The best scores are made with three 15-shot groups about 1.5 MOA in size.

 

[Llama Bob]

There's a potential problem with that rule of thumb - namely that as you shoot more rounds per group, the group size will increase but your confidence in the location of the center of the group will also increase.

This leads to the counter-intuitive situation where it sometimes makes sense to make a sight correction based on a large group, but not a small one, if the group is large because it contains many shots.

However, in any situation where shooter or environmental factors are likely in play, it's probably a good rule.

 

[Bart B.]

Last time I checked, both shooter and environmental factors are always in play.

Don't all us shoot in the earth's environment? And neither is perfectly still all the time when shooting is happening.

 

[lysanderxiii]

In my book there's a very simple definition: When any possible change to sight adjustments won't bring point of impact closer to the point of aim, it's zeroed.

true

Last time I checked, both shooter and environmental factors are always in play.

Don't all us shoot in the earth's environment? And neither is perfectly still all the time when shooting is happening.

That is the one thing they never did on the moon that I wished they would have, shot a pistol, or something. Just for sh!ts and grins....

But, someone in the military has thought about it. Somewhere out there is a copy of "Military Operations on the Surface of an Extraterrestial Body" . . .

 

[lysanderxiii]

There's a potential problem with that rule of thumb - namely that as you shoot more rounds per group, the group size will increase but your confidence in the location of the center of the group will also increase.

This leads to the counter-intuitive situation where it sometimes makes sense to make a sight correction based on a large group, but not a small one, if the group is large because it contains many shots.

However, in any situation where shooter or environmental factors are likely in play, it's probably a good rule.

You don't have to get the opinion of every single person who ever bought a bottle of Brand Y Catsup to know if it is a good product and/or how it could be improved.

Same with group sizes. Just get a statistically relevant number, probably more than three and less than 20.

 

[horsey300]

You don't have to get the opinion of every single person who ever bought a bottle of Brand Y Catsup to know if it is a good product and/or how it could be improved.

Same with group sizes. Just get a statistically relevant number, probably more than three and less than 20.

19 is acceptable then

 

[LoonWulf]

Shoot, im 9 rounds off....

 

[Bart B.]

Just get a statistically relevant number,

How many is that?

Depending on ones level of confidence desired it'll vary a lot. Arsenals used 270 shots with rifle ammo for a test of its accuracy. Then group center was calculated so radius from there to each shot hole could be calculated to get the mean radius. Typically, extreme spread across two widest shots was 4 to 5 times mean radius. About 40% of the shots were in the middle 40% of extreme spread, 30% in the next larger 30% area, 20% of the shots in the next one and 10% in the outer 10% of the extreme spread. The guy at Lake City Arsenal that mentioned this to me said it was the 10-20-30-40 rule of thumb sometimes used.

 

[Laphroaig]

for windage though, a little right/left offset I am afraid could hamper my ability to learn how to read the wind by giving me a false indication when shooting for a 5" plate at 600yds.

would YOU tweak the windage a little using the ability on my scope to try and go "in between" the .1 mil clicks to line my windage up a little better.
I will be verifying at the range from the same bench type position I will be shooting at long range with. my hesitation is that I am not really familiar with that adjustment and I could end up overdoing it, requiring a few adjustments and headache when what I have is more accurate than I have ever been able to achieve.

I don't know if you've considered this, but unless 1) your scope is mounted perfectly vertical with your rifle, and 2) your rifle is held perfectly vertical when shot at distance, there will be a change in your windage zero as your scope elevation is dialed up to hit the target. Unless you are very fortunate, probably neither 1) or 2) is humanly possible. You better know what that effect is and correct for it before you try and apply an actual wind correction.Therefore, you need to establish a no wind zero for your elevation DOPE.

One way to do that is to apply your long range elevation DOPE while shooting at a reduced distance, and on a relatively calm day, where wind won't affect your impact. For instance, if you have to dial in 4 mils of elevation (I'm ball parking here) for a 600 yd. zero, you would shoot a target at 50 or 100 yds with that elevation setting , and measure the horizontal offset from the aim point. That is your no-wind windage correction corresponding to that elevation setting. Record those and convert to mils to apply when dialing in for longer distances.

 

[Bart B.]

for windage though, a little right/left offset I am afraid could hamper my ability to learn how to read the wind by giving me a false indication when shooting for a 5" plate at 600yds.

Few can make accurate wind corrections at any range past 400 yards for the first shot fired that's within 1 MOA of being exact. Two reasons. First one is the wind closest to the firing point has a greater effect than the wind near the target on drift from cross winds.


Wind in first third, about 44 inches at 1000 yards.

Wind in last third, about 16 inches at 1000 yards.

Second one is, wind above the line of sight is faster than in the line of sight; ground terrain slows the wind not much for flat terrain but quite a bit in wooded areas or where lots of buildings are. People erection wind powdered turbines several dozen feet above ground have a formula they use to calculate wind speed at the turbine blades heights from what it is a few feet above ground level.

 

[coloradokevin]

I grew up with my father taking a deer rifle out once a season or so, firing 3-5 shots and as long as it was within a few inches it was "good enough"

I now am trying to get into a little more long range, precision stuff. so I got a really well made 308 win, SMK's and made up a good load. when do you call it "good enough" for a 100yd zero on a target gun?

attached is a picture from over the weekend. 5 shots each group. the group on the left i fired first, saw it favored the right side so I came .1 mil left. now the left side is favored. I need to come right about .05 mils (vortex razor gen II, you can adjust in between "clicks") and maybe .02 mils up.

group on the right, the lowest shot I pulled, so I am ignoring that one for center of group/zero. the stickers are 1"View attachment 228312

You're good... eventually you just have to call it good enough with your zero, because you very well may end up (as you did) being "between clicks". I shoot my .308 Win regularly to 800+ yards, and run my .260 Remington out to 1,500 yards. My zeros aren't any better than yours, honestly.

And, the old "zero above the dot" thing (MPBR) is for hunters who aren't running field adjustable turrets and dope charts. For precision shooting, a center zero is exactly what you want.

 

[Bart B.]

Another issue not mentioned so far in getting exact zero set on the sight is how repeatable we aim the rifle without any cant. For every degree of cant, bullets strike to the side of point of aim about 1/60th of bullet drop at target range. If bullet drop at 1000 yards is 360 inches, that's 6 inches; 6/10ths MOA. At 100 yards, it's about impossible to resolve.

It's easy to keep cant repeatable across several shots using a scope. Not so with metallic sights; those for longer ranges often have a spirit level on the front sight. Knowing how much bubble shift causes 1 MOA horizontal change in bullet impact is helpful in team matches. You can move bullet impact horizontally canting the rifle a degree or two. Elevation change is negligible; 1/18th inch for the above criteria at 1000 yards.

 

[Driftertank]

...different time of day can change my zero..." Nope. That's your eyes.

I'll believe that. Or the specific coloration/shape of the target. Or mirage. Slight variation in downrange wind. Perhaps incorrect parallax adjustment. Or i changed my position slightly. Or it warmed up, or cooled down.

I dont shoot benchrest; generally prone or sitting braced. My eyes arent the greatest, i have astigmatism in both. There's a million little factors that influence where my point of aim coincides with my point of impact.

I'm a pretty fair shot, but not the greatest. I would consider the OP's last group perfectly zeroed for all practical intents and purposes. Better group than i typically manage.

But my point is, theres a lot of factors that effect point of impact, and unless he will be shooting in a climate-controlled, windless 1000yd indoor range, his POI will probably change more with ambient conditions than his distance-from-center in the last pic. Just my experience. I figure thats real goodd zero. And damn fine shootin/loading/equipment.

 

[Bart B.]

Light from the target in a given environment goes through the sight then into the aiming eye equal for everyone. Doesn't matter what their vision quality is. Some people will see a given aiming error more clear and less distorted than others. It's amount doesn't change.