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xsquidgator
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24/08/2019 7:23 pm  

How often do you verify your rifle's zero?  Do you have any kinds of specs for yourself on how close is "good enough"?

I suppose the "right answer" that an expert would give would depend on the application, after all, if your sights/optic are on close enough for you to be able to hit the target when you do all the other stuff right, that should be good enough.

I started thinking of this today- I took two ARs with low power variable optics to the range for a quick several shots with each to verify zero.  I'm shooting a carbine type match this weekend (a run n gun with rifle shots out to about 400 or 500) and I figured everything's good since it was the last time I shot these rifles, but why not check while there's time, just to be sure?  The same type of deal I'd do if I was taking a carbine class, show up with a zero'd rifle.  Since I have extras, I check the main one and the backup one brought along in case the main one goes down.

I noticed over the past 5 years or so of doing this that my zero seems to change a little bit from time to time, say 2 MOA or less.

Not enough to really matter for close distances say 100-200m, but enough to probably start mattering further out.  I've seen this with my EOTech (and am aware that they became undesirable when it came out they could have zero problems off > 4 MOA especially when they get really hot or really cold) but also with somewhat decent optics like Vortex and Burris.

In today's case, I dialed in a 1 MOA left correction based on the quick zero check.  Of course there's another problem with doing this the way I did, the LPVO scopes are zero'd at 100m and I know with an AR they're about 6 MOA low (1.5 inches or so) at 25m... but, I really should have just shot a target at 100m to eliminate that pecadillo.  I am thinking of going back to the range tomorrow to redo that and get just a little more shooting in before the match so maybe I'll do that.  I may check this zero off of sandbags too, today's sort of quick effort was from prone with a sling, theoretically just as good but practically not as good as using a rest.

What do you all do and if you checked and found you were 1 or 2 MOA off, would you adjust your zero and kind of expect it to change a little over the course of several months?  I'm not talking high precision application, just being able to hit a steel silhouette target out to several hundred yards in sort of a practical rifle situation.  What do you all think?


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Diceman624
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25/08/2019 6:40 am  

My general policy for rechecking zero is if I ever change any part of the sighting system, the weapon must be rezeroed.  That applies for BUIS and optics.  Unfortunately, I haven't yet encountered a situation like you described yet.  However, I suspect that going between indoor and outdoor ranges will demonstrate how changes in climatology will affect ballistics.  Given the changes in daytime highs and the humidity where I live, I wouldn't find it beyond imagination to find a rifle zero change.  If I found one, I would reset the zero to what I intended it, and drive on.

When it comes to longer range zero checks, like say the 200m part of the 50yd/200m zero, I'm currently hamstrung by the fact the range I'm currently a member of only goes out to 100yds.  When I re-up my membership at the local outdoor range, I'll have access to a 200yd range.  I mean to get better at validating such combination zeroes in the future.

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Matt
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25/08/2019 8:34 pm  

So, from an academic standpoint, doing a re-zero is required when any of the major elements of the zero change.

  • Weapon
  • Ammunition
  • Conditions

Like @diceman624 said, you might be experiencing some shifts due to conditions such as light, temperature, or pressure. It's pretty well known that as it gets brighter, sights tend to adjust up ("Sun up, sights up"), and adjustment down as it gets darker.

Now, practically, with the amount that I tinker with my weapons and move sights back and forth, I feel like I'm doing a quick zero procedure every time I go to the range. It's also not practical to adjust zero every time I change ammo, because the stuff I practice with isn't usually what I'm going to use in a match or defensive purposes. So I pick the one that I'm most likely to use, and zero with that.

Over time, if you're documenting things, you might notice some consistent patterns in the zero shifts and can automatically dial those changes as the condition changes.

"Man is still the first weapon of war" - Field Marshal Montgomery


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xsquidgator
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26/08/2019 9:42 am  

My original post was Saturday, since I had some time yesterday, I went back to the range and this time just checked things out at 100m.

At 100m on Sunday, I was still off by ~ 2 MOA or so but in the opposite direction from the day before when tested at 25m, i.e. the Sunday corrections I dialed in more or less cancelled out the Saturday corrections.

I agree with changing conditions could change the zero, although other than sun and temperature varying, I can't think of anything really changed.  From talking with a number of PRS (precision rifle shooters) guys, your point of impact will definitely change if the bore is cold and clean, particularly the clean.  The guys who may need to professionally make an important shot on-demand generally thus do not routinely clean out their bores when cleaning the rifle.

With my own experience over the past 5 or so years or so, I've noticed that with an AR-15 the zero may shift as much as 2 MOA (like I seem to have experienced here) due to whatever it is, different conditions, time passing, I'm not sure what.  For carbine type shooting sports this may not matter a whole lot if the distances aren't that far (perhaps 200 yards or less?)  I have to fess up that there's a good chance the variability is me not getting consistent cheek weld (sight alignment) or something similar, it's probably not the rifle/optic.

As my understanding and experiences evolve, I think:

1) I will continue to check zero and preferably at the zero distance (100m for LPVO, maybe 25m/300m or 50/200m for a red dot zero) shortly before expecting to use the rifle for a match or a class.  I didn't use to think about checking zero like this, rather I'd kind of forget about it once I thought it was set.

2) If I'm zeroing a rifle or optic for the first time, I might use prone with a sling or sandbags.  But for checking to be sure zero is good as precisely as possible, I think I'll stick with a benchrest and sandbags.  There are a few tricks we can learn from the PRS guys about this kind of thing such as putting the rifle on sandbags supported fore and aft on the rifle, and you adjust the muzzle elevation by gently squeezing and relaxing the squeeze on the rear sandbag.  As an Appleseeder I/we are supposed to be able to use prone position with loop sling to be just a rock, and while that technique can be very useful, in my case at least it just isn't as steady as bags and a bench.


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John_Simpson
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26/08/2019 2:01 pm  
Posted by: @xsquidgator

The guys who may need to professionally make an important shot on-demand generally thus do not routinely clean out their bores when cleaning the rifle.

I actually have to take exception to that statement. What you describe has been a trend in the past but nowadays more often than not this whole "cold bore" myth can be eliminated by finishing your bore cleaning by swabbing with patches soaked in rubbing alcohol. Failing to do this the leftover traces of cleaning solvent acts as an accelerant throwing off the zero which is why this step is included in the cleaning section of my latest book as well as my previous book (The Snipers Notebook).


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Sunshine Shooter
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26/08/2019 5:11 pm  

Your changing zero might be from temperature alone.  Different materials shrink & expand differently along the same temp swings, so your aluminum upper & scope base may expand differently than your steel barrel, or the scope internals.  What you describe sounds like a bit much to only be the fault of temperature differences a day apart.

What were the ambient conditions?  Did your gun go from AC straight to the range, or did it sit in the sun on day and not the other?

"Good judgement comes from experience, and experience comes from bad judgement"

progunmillennial.wordpress.com


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Jerry
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31/08/2019 9:23 am  

Here in northern Minnesota re-zero is common with extreme temp changes. I know I have to re-zero for winter and again for spring. Slight variations in between as well due to temp swings at Service matches on your 5 sighters.

Thanks for the tip @john_simpson


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Matt
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31/08/2019 12:14 pm  
Posted by: @john_simpson
Posted by: @xsquidgator

The guys who may need to professionally make an important shot on-demand generally thus do not routinely clean out their bores when cleaning the rifle.

I actually have to take exception to that statement. What you describe has been a trend in the past but nowadays more often than not this whole "cold bore" myth can be eliminated by finishing your bore cleaning by swabbing with patches soaked in rubbing alcohol. Failing to do this the leftover traces of cleaning solvent acts as an accelerant throwing off the zero which is why this step is included in the cleaning section of my latest book as well as my previous book (The Snipers Notebook).

Great insight, John! I feel like the whole question of the "cold bore" myth is worthy of an article in of itself.

"Man is still the first weapon of war" - Field Marshal Montgomery


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xsquidgator
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31/08/2019 12:31 pm  

@john_simpson

Thanks for the comment and the information, I will have to check this out.

Sunshine Shooter and Jerry, thanks for sharing your experience.  Temp changes may have played a part in this and I'll pay closer attention to it going forward.

This post was modified 4 months ago by xsquidgator

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Jerry
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31/08/2019 1:04 pm  

Zero change is a interesting topic.

Here is a quote out of linked article on the subject.

There is a rule of thumb. For every 20 degrees difference (and we deal in Fahrenheit here) from the temperature at which you zeroed, you can expect a drop of 0.5 to 1.0 m.o.a.

https://www.rifleshootermag.com/editorial/environmental-factors-shooting/83473

Given ample time it'd be a good test to prove out.


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John_Simpson
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04/09/2019 1:27 pm  
Posted by: @rto-jerry

Zero change is a interesting topic.

Here is a quote out of linked article on the subject.

There is a rule of thumb. For every 20 degrees difference (and we deal in Fahrenheit here) from the temperature at which you zeroed, you can expect a drop of 0.5 to 1.0 m.o.a.

https://www.rifleshootermag.com/editorial/environmental-factors-shooting/83473

Given ample time it'd be a good test to prove out.

Sorry to have to tell you but the "rules of thumb" in that article are horse crap. That 20 degree rule for temp and that 20% rule for humidity were debunked a long time ago. About the only thing he gets right is that humid air is less dense than dry air.

I'm attaching a chart I made for my latest book showing the real downrange results of a 20 degree change from your zero temperature. If you follow his happy little rule of thumb you'll miss. To correct for a 20 degree change in temperature you'd need a scope with elevation adjustments in 1/100th of a minute of angle.

Those little "rules of thumb" are like Dracula. Put a stake in his heart and he still comes back for the sequel.


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Jerry
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04/09/2019 9:20 pm  

@john_simpson

Thanks for debunking pure rubbish of that article.


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