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Old August 28, 2013, 11:40 AM   #1
craZivn
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A Question About My Shot Grouping: Where is Zero?

Seems like just about every time I shoot a 3-shot grouping, two of the shots are close together and one of them strays quite a bit. Is there a scientific reason for this, besides the fact that I'm not exactly the steadiest shot on the block?

And more importantly, where do I judge the "zero" to be here? Do I average the center of the three shots, or assume the odd one to be a "fluke" and take the two close ones as being the POI? Or should I be shooting more shots per group?



Ammo is PMC Bronze 55 gr. .223, distance is 100 yards. Shooting from a standing/laying sort of rest. P.S. Any tips on how to get that grouping smaller would be appreciated. Rifle is an AR w/16" barrel, Weaver 1-3 power scope.

Thanks,
Ivan
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Old August 28, 2013, 11:56 AM   #2
allaroundhunter
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A Question About My Shot Grouping: Where is Zero?

Is the "off" shot always the first? Or last? Or is it random?


To get an idea for a zero with that gun I would shoot a 10 shot group and go from there.
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Old August 28, 2013, 12:05 PM   #3
Rikakiah
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Quote:
Is the "off" shot always the first? Or last? Or is it random?
This. If it's the first, cold bore vs warm bore? Otherwise, in my amateur experience, you may be flinching a bit for some reason? Lock the rifle down (benchrest/sandbag/etc) and confirm.
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Old August 28, 2013, 12:13 PM   #4
Brian Pfleuger
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Generally speaking, draw a triangle with your shots at the corners. The center of the triangle is the "zero". Once you have the triangle, draw a line from each shot to the center of the opposite side and where the lines intersect is the "zero".

You can download the free software "OnTarget" too which, IIRC, shows you where the center of your group lies.

The cause of the "flyer" in your group could be (at least):

Random Chance
You making a bad shot
Inconsistent ammo
Barrel heat
Wind

Consider for a moment that the two that are near each other each have an equally good probability of landing there randomly as did the one that's further away. 3-shot groups are notoriously unreliable but can be helpful in establishing if a load is "bad". Not nearly as good for determining if it's "good".
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Old August 28, 2013, 01:40 PM   #5
Rikakiah
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Maybe try a bigger sample size, too, and see what your average is there, but really about the only way you can know for sure is to lock down the rifle and take any human movement out of the equation.
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Old August 28, 2013, 01:49 PM   #6
ripnbst
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Yeah, shoot statistically larger sample groups. Since its an AR I'd shoot 5 at a bare minimum but really I'd want to see something like 10 shots for a good "group".

Remember to wait between shots to allow everything to "settle in" thermally. I'd also advise waiting 10 minutes after you get out of the car to allow everything to come to ambient temp.

I would also point out that it is good to run a couple shots through the gun first as "foulers" before doing a grouping. If the gun is clean for the first shot and gets progressively more dirty that *can* affect POI. Again, being an AR this is easy to do. Run a few shots through it and then start your grouping.
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Old August 28, 2013, 01:50 PM   #7
Brian Pfleuger
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Locking down the rifle only sights it in for being locked down. If it's not going to be shot that way when it matters (at game or whatever) it should not be sighted that way.

It is a common misconception that different shooters will shoot the same gun to a different Point of Aim because they see/use the sights differently. The light going through the sights (iron or optics) doesn't care who sees it. The gun shoots different for different shooters because they hold it different and manage the first fractions of a millisecond of recoil differently. Locking it down WILL cause a different Point of Impact than firing from a rest against your shoulder which will also be different that firing from free-hand or from a sling.
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Old August 28, 2013, 04:32 PM   #8
MarkCO
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Most common ARs will toss a flyer on the first, or the last, or both rounds from a magazine. If it is the first, try locking the bolt back and using the bolt release to chamber the round. I'll shoot 3 5 round strings from 3 loadings starting form bolt lock and the last locking the botl open. I put the first round of each on a left target, the middle three on the middle target and the last three on the right target. Let's me know if that particular specimen is prone to a flyer on the first or last round. Doing this from a bench helps provided you don't chase the POI and keep the exact same hold on every shot.
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Old August 28, 2013, 08:05 PM   #9
craZivn
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Wow, tons of great advice here! I don't know which shot in sequence is the flyer, my scope is only a 3-power max and at 100 yards I can't see the bullet holes.

So I will fire one or two pre-grouping shots (not really "foulers" as the rifle doesn't get cleaned in between range sessions), then do a ten-shot group and see where my center of POI is. And will keep my rate of fire down so heat doesn't build up too fast.

Thanks much for the pointers! They were exactly what I was looking for. Provided they work.

Ivan
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Old August 28, 2013, 09:00 PM   #10
FtrPilot
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Quote:
I don't know which shot in sequence is the flyer.
Suggest buying or borrowing a spotting scope.

I am not trying to be sarcastic. A lot of rifles are known for throwing an outlier. Knowing what your rifle does is critical to shooting good groups. The ability to "score" each shot immediately after you shoot it is important in that analysis.

Last edited by FtrPilot; August 28, 2013 at 09:06 PM.
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Old August 28, 2013, 09:22 PM   #11
Rikakiah
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My point on locking it down is to remove variables to find out what the issue is. If they're all in a tight little group from a solid position, you can pretty much factor out barrel/gun issues. It sounded like he was more concerned with why there was a flier than specifically dialing in his zero. Especially getting results like this, I'd personally be interested in what the GUN can do, then see what *I* can do with the gun.
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Old August 28, 2013, 09:25 PM   #12
Rikakiah
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Re: A Question About My Shot Grouping: Where is Zero?

Quote:
Originally Posted by FtrPilot View Post
Suggest buying or borrowing a spotting scope.
And maybe bring a buddy to spot for you. Will save you the change from rifle to spotting scope, which will not only speed up the process but also prevent any change in your hold/stance that may skew your results.
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Old August 28, 2013, 09:26 PM   #13
Willie Lowman
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Quote:
Yeah, shoot statistically larger sample groups. Since its an AR I'd shoot 5 at a bare minimum but really I'd want to see something like 10 shots for a good "group".
Also, try better ammo. PMC isn't known for it's accuracy.
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Old August 29, 2013, 08:26 AM   #14
kraigwy
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Forget the 3 or 5 shot groups, shot 10-20 rounds to get a zero.

After shooting (the more rounds the more accurate the zero) draw a line from 12 to 6 o'clock, then draw a line from 9 to 3 o'clock.

Count the shots in each quarter. Adjust and do it again. When you have an equal number of shots in each quarter you have your zero.

This works if you're a good shot or bad shot. You may have a pie plate size group but if you get an equal number of shots in each quarter, you're zeroed.
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