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Groups size and distance


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#1 Stubb

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Posted 26 January 2016 - 12:37 PM

Any reason to think that ammo that groups well at 10 or 15 yards wouldn't group well at 25 or 50? Outside of obvious problems like tumbling. I've been blaming poor technique on my part but wondering if it could be ammo related, particularly related to shooting coated bullets.


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#2 Sprewell

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Posted 26 January 2016 - 12:47 PM

Yes.  If you had a perfect mechanical rest I would expect a fifty yard group to be more than five times bigger than a ten yard group.  In some cases a great deal more than five times bigger.  Any disturbance to the bullets flight is not linear, it gets worse and worse exponentially.  In my opinion and experience.


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#3 GuanoLoco

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Posted 26 January 2016 - 01:21 PM

I've always assumed my near-sightedness was one possible explanation for groups opening up with increasing distance more than I would mathematically expect.


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#4 Miculek is a Noob

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Posted 26 January 2016 - 01:33 PM

Yes. If you had a perfect mechanical rest I would expect a fifty yard group to be more than five times bigger than a ten yard group. In some cases a great deal more than five times bigger. Any disturbance to the bullets flight is not linear, it gets worse and worse exponentially. In my opinion and experience.


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#5 Stubb

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Posted 26 January 2016 - 01:35 PM

I've always assumed my near-sightedness was one possible explanation for groups opening up with increasing distance more than I would mathematically expect.

 

I'll be addressing that possibility early next month.



#6 ZackJones

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Posted 26 January 2016 - 01:39 PM

Look at the big brain on Sprewell!


He googled it.
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#7 GuanoLoco

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Posted 26 January 2016 - 02:16 PM

I'll be addressing that possibility early next month.

 

Sprewell's explanation is easier to stomach.  Suckitude seems another likely answer.


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#8 aceinyerface

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Posted 26 January 2016 - 02:21 PM

I have found that it is never the gear.



#9 Sprewell

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Posted 26 January 2016 - 02:23 PM

A good test for suck is to come up with a target that looks the same at 50 yards as it does at 10 or 20.  It's very difficult to shoot accurately if you can't get a good sight picture on your chosen target.  To kind of state the obvious.



#10 GuanoLoco

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Posted 26 January 2016 - 02:47 PM

Funny that you mention that. I once shot a 1" 5-shot group with an AR-15 using sandbags and an unmagnified, dimmed down Eotech at 100 yards - but the target was a very visible large (12") flat black circle.

My only explanation is that I could actually see the circle.
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#11 Stubb

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Posted 26 January 2016 - 03:43 PM

Will print out some NRA B-8 targets to shoot this weekend.



#12 Vagetarian

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Posted 26 January 2016 - 04:32 PM

I've always wanted to get a Ransom Rest to test the accuracy of gun and ammo without me fucking it all up.  I had some questionable ammo a couple of years ago and it was just that.  Fliers every third round.


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#13 ToddKS

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Posted 26 January 2016 - 06:11 PM

Any reason to think that ammo that groups well at 10 or 15 yards wouldn't group well at 25 or 50? Outside of obvious problems like tumbling. I've been blaming poor technique on my part but wondering if it could be ammo related, particularly related to shooting coated bullets.

I experienced this with plated bullets. Loads group fine at 15 but at 25 not so good. Jacketed bullets solved the issue. Tested it enogh times that I have no doubt the bullet was the issue.

This was in a G17.

Get some Hornady HAP and test with those and see if the issue goes away.

#14 not that bryan

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Posted 26 January 2016 - 06:13 PM

Any reason to think that ammo that groups well at 10 or 15 yards wouldn't group well at 25 or 50? Outside of obvious problems like tumbling. I've been blaming poor technique on my part but wondering if it could be ammo related, particularly related to shooting coated bullets.

10 yards is short enough distance to cover up a lot of mistakes, both mechanical (gun /ammo) and shooter induced.

I shoot targets all the time for work (variety off guns from subcompact all the way up to competition guns) that have to shoot into a 2 inch or smaller circle out to 15 yards. Using ammo of various quality. At 10 yards I almnost never have problems. 15 yards get harder and ammo starts to be noticeable, as some group tighter than others.

#15 not that bryan

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Posted 26 January 2016 - 06:17 PM

Try some factory ammo to rule out the ammmo. If your groups are noticeably smaller with factory (jacketed) ammo you know ammo is the issue.

#16 Stubb

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Posted 26 January 2016 - 07:51 PM

I have a couple HAPs left over and a few thousand PDs. Group-shooting fun awaits!



#17 busdriver

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Posted 26 January 2016 - 08:13 PM

Without accounting for any non-linear dispersion, a gun/load that groups .8 inches at 10 yards should group 2 inches at 25.  Bump the 10 yard group up to 2 inches and you're looking at a 5 inch 25 yard grouping.  I would imagine that shooter errors are very much non-linear, making the longer distance groups that much worse.

 

Well, assuming I did that math shit right.  I did damn near fail calc in college.....



#18 RDS

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Posted 02 February 2016 - 02:04 PM

Actually....

If we have two factors--the shooter and the gun, and assume each gives a random normal (gaussian) bell curve for errors or shot spread, then to combine those errors, you use the variance or standard deviation squared. There can be regions were one distribution dominates the other causing non linear results. Throw in non normal distribution and it goes to hell pretty fast.

If you go by a single spread. than the group size (radius or diameter) increases directly with distance. If you go from 1 inch at 20 yards then it will be 2 inch at 40 yards at 4 in at 80 yards. The area of the group increases with the square of distance. Basically to first approx sprewell and bus are correct.

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#19 GuanoLoco

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Posted 02 February 2016 - 02:41 PM

Actually....
If we have two factors--the shooter and the gun, and assume each gives a random normal (gaussian) bell curve for errors or shot spread, then to combine those errors, you use the variance or standard deviation squared. There can be regions were one distribution dominates the other causing non linear results. Throw in non normal distribution and it goes to hell pretty fast.
If you go by a single spread. than the group size (radius or diameter) increases directly with distance. If you go from 1 inch at 20 yards then it will be 2 inch at 40 yards at 4 in at 80 yards. The area of the group increases with the square of distance. Basically to first approx sprewell and bus are correct.


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Anyhow, that looks like a linear increase with distance to me. Remember, Maths don't work on Doodie. Neither does logic. Including mine.
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#20 Shithead23

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Posted 02 February 2016 - 03:19 PM

Yep...try some factory ammo.  I'll use hornady with xtp bullets for reference.

 

I use SNS coated bullets for practice and match ammo.  I've kept good groups at 5o yards off of a bench...

25 yards i'll see 2" groups with 1.180"load length 4.2 solo 1000 in my fortay.


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