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Old February 5, 2011, 04:11 PM   #1
gregjc9
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What does a grouping like this mean?

I was testing some more 223 loads from my AR today, and one of the loads tested, the 5 shot group was a little peculiar. All 5 rounds were basically lined up vertically. It's hard to see, but 2 are in same hole. Same powder, etc. Maybe I wasnt getting behind the scope consistently each time? I would expect to see the group more scattered.

RRA AR, 20" 1:8 barrel, 75gr Hornady HPBT, 2.250 COAL, H335 21.6gr @ 100yds.
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Old February 5, 2011, 04:32 PM   #2
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Assuming a consistent hold, you might just have to increase the charge a small amount.
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Old February 5, 2011, 04:37 PM   #3
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"Vertical stringing", a common effect of a thin, light barrel heating up under rapid fire.
For some reason gas guns are particularly prone to it. Try (not kidding here) making the handguard less tight at the front end attachment point ( gas block)
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Old February 5, 2011, 04:43 PM   #4
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Wogpotter, makes sense, but mine is a RRA Predator Persuit upper, bull S/S barrel. All shots were slow fire about a minute apart. The barrel may have gotten warm, but definately not hot, and definately not rapid fire. The hand guard is a free floating Hogue tube.

Oh, and I was using a benchrest as well.
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Old February 5, 2011, 05:21 PM   #5
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since you are using a bull bbl, thats out of the picture I suppose. Excessive trigger sear tension could be a culprit. Also, if your primers are not consistently seated, or your firing pin spring is loosening, this may occur. Are your charges weighed individually? or do you use a thrower? Do you crimp? Are you using bullets the are good quality and consistent weight and dimensions? It is a velocity deviation that causes the vertical stringing, and oh so many factors can cause that.
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Old February 5, 2011, 05:32 PM   #6
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Looks like it's your breathing to me.
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Old February 5, 2011, 06:08 PM   #7
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Now that I know what it's called, I found this article. Gives me a lot to think about.

The bullets are all high grade, 75gr Hornady HPBT. The suggestion on my breathing might be it. I try to breathe half out, hold, then squeeze trigger, but I know I have a lot to learn in this area. Thanks for the info.
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Old February 5, 2011, 06:21 PM   #8
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Quote:
I try to breathe half out, hold, then squeeze trigger, but I know I have a lot to learn in this area.
Try shooting during the natural respiratory pause between breaths, that way it's always consistent.
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Old February 5, 2011, 06:42 PM   #9
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breathing is the first thing to check
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Old February 5, 2011, 06:57 PM   #10
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I'm not so sure about breathing as much as trigger control. A near perfect vertical string in my experience doesn't seem to relate to a string like that. It would be more of a slant. Heartbeat does the same. Not 100% certain it's your problem, but that's my take.
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Old February 5, 2011, 07:11 PM   #11
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As long as it helped you to have a place to look for answers.
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Old February 6, 2011, 03:53 AM   #12
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Greg, what is the group size on that one? Besides the vertical stringing it seems to be a decent group. Your groups seem to be shrinking the mire you show your results.
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Old February 6, 2011, 08:56 AM   #13
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Lloyd, that group was a .99"

Breathing and/or trigger control. I know those are two areas I need to work on. I shoot pistols A LOT, but that's a different game than this. I'll work on them more next week. Thanks for the suggestions.
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