What does a grouping like this mean?

gregjc9 · February 5, 2011, 04:11 PM

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.

Rifleman1776 · February 5, 2011, 04:32 PM

Assuming a consistent hold, you might just have to increase the charge a small amount.

wogpotter · February 5, 2011, 04:37 PM

"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)

gregjc9 · February 5, 2011, 04:43 PM

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.

flyboyjake · February 5, 2011, 05:21 PM

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.

hoytinak · February 5, 2011, 05:32 PM

Looks like it's your breathing to me.

gregjc9 · February 5, 2011, 06:08 PM

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.

hoytinak · February 5, 2011, 06:21 PM

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.

jackpine · February 5, 2011, 06:42 PM

breathing is the first thing to check

**Shane Tuttle** · February 5, 2011, 06:57 PM

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.

wogpotter · February 5, 2011, 07:11 PM

As long as it helped you to have a place to look for answers.

LloydXmas250 · February 6, 2011, 03:53 AM

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.

gregjc9 · February 6, 2011, 08:56 AM

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.

February 5, 2011, 04:37 PM	#3
wogpotter Senior Member Join Date: September 27, 2004 Posts: 4,811	"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) __________________ Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”? Elderly Hunter: “That's dashed unsporting. Probably Belgium.”

February 5, 2011, 04:43 PM	#4
gregjc9 Senior Member Join Date: June 30, 2008 Location: Northern Va Posts: 501	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. __________________ ΜΟΛΩΝ ΛΑΒΕ Greg

February 5, 2011, 06:08 PM	#7
gregjc9 Senior Member Join Date: June 30, 2008 Location: Northern Va Posts: 501	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. __________________ ΜΟΛΩΝ ΛΑΒΕ Greg

February 5, 2011, 06:57 PM	#10
Shane Tuttle Staff Join Date: November 28, 2005 Location: Montana Posts: 9,443	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. __________________ If it were up to me, the word "got" would be deleted from the English language. Posting and YOU: http://www.albinoblacksheep.com/flash/posting

February 5, 2011, 07:11 PM	#11
wogpotter Senior Member Join Date: September 27, 2004 Posts: 4,811	As long as it helped you to have a place to look for answers. __________________ Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”? Elderly Hunter: “That's dashed unsporting. Probably Belgium.”

February 5, 2011, 04:32 PM	#2
Rifleman1776 Senior Member Join Date: April 25, 2010 Location: Arkansas Posts: 3,309	Assuming a consistent hold, you might just have to increase the charge a small amount.

February 5, 2011, 05:21 PM	#5
flyboyjake Senior Member Join Date: February 19, 2010 Posts: 135	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.

February 5, 2011, 05:32 PM	#6
hoytinak Senior Member Join Date: July 5, 2006 Location: Texas Posts: 5,721	Looks like it's your breathing to me.

February 5, 2011, 06:42 PM	#9
jackpine Senior Member Join Date: November 24, 2010 Posts: 351	breathing is the first thing to check

February 6, 2011, 03:53 AM	#12
LloydXmas250 Senior Member Join Date: October 6, 2009 Location: So Cal Posts: 334	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.

February 6, 2011, 08:56 AM	#13
gregjc9 Senior Member Join Date: June 30, 2008 Location: Northern Va Posts: 501	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. __________________ ΜΟΛΩΝ ΛΑΒΕ Greg