Odd Grouping on my Target

JefferS · May 5, 2014, 01:49 PM

Got a weird pattern this weekend.

.30-06
IMR-4350, 54.7 gr
Nosler BT, 150 gr
100 yd

It seemed like shots moved from left to right.

What are the theories on my problem?

Limit the theories to ones related to my Sportsman 78, .30-06, or we'll overload the server.

Bart B. · May 5, 2014, 02:07 PM

I've seen that happen when the (right handed) shooter twists his body clockwise behind the rifle as it rests on something atop a bench. A bit more for each consecutive shot.

Is this repeatable?

If the rifle is fit and screwed together correctly, I think its a shooter position or rifle holding that's not repeatable from shot to shot. Let someone else shoot it then see what happens.

Jim243 · May 5, 2014, 02:24 PM

The screws are coming loose on your mounts, not the rings but the mounts on the rifle. (most likely the front one) Retighten using some lock-tight.

Jim

eldermike · May 5, 2014, 03:11 PM

I have had one scope go bad like that, it drove me nuts for a while. I did a new bed job, cast the chamber, even had the crown cut then somone told me to try a different scope....that was it.

Brian Pfleuger · May 5, 2014, 04:06 PM

My first thought is, do you actually KNOW that those shots moved right to left consecutively or is it just an assumption?

JefferS · May 5, 2014, 05:25 PM

I know the first shot was the left one. I can't guarantee 100% that the rest were moving to the right sequentially, but that was my impression when I finished. I really felt that the last shot was the furthest away from the first because I thought to myself, "Did I pull that much?"

I was really only focusing on getting a group at the time and trying to aim at the X consistently, and wasn't keeping track of the individual shots (lesson learned).

mikld · May 5, 2014, 06:36 PM

How many of those horizontal groups did you get?

Brian Pfleuger · May 5, 2014, 07:14 PM

Without absolute certainty of which shots are which, you'd be better off reading tea leaves.

JefferS · May 5, 2014, 07:28 PM

My tea leaves drop right to left.

Jimro · May 5, 2014, 08:09 PM

Whether or not the shots impacted in a linear manner is irrelevant to the linear dispersion pattern.

The groups indicate that something is shifting. The two most likely culprits have already been identified, shooter position and optic repeatability.

Tighten the bases, tighten the rings, move your windage knob a turn around, then a turn back to see if the springs have taken a set or replace the scope with a known good unit.

If consistent body position and a new scope don't fix the issue, I would recommend a powder charge change to see what that does, ensuring the barrel is free floated.

Jimro

Brian Pfleuger · May 5, 2014, 08:31 PM

Of course it's relevant!

If they're not consecutive it could be any number of random reasons. If they are consecutive, it's a single cause (or random chance).

Horizontal groups have causes, horizontal "walking" has other causes. They're not necessarily the same.

Jay24bal · May 5, 2014, 11:36 PM

Maybe it is too obvious to even ask, but was it windy? I was also out shooting this past weekend in OH, and we had sustained winds in the 20's with gusts into the mid-high 30's.

If we call the far left a "flyer" or you pulled it, it is not hard to imagine a 2" group in windy conditions like I had here, especially since you were testing loads and this very well could be a bad load for the gun.

I only ask because it was windy as heck here this weekend, and the other four besides the flyer are within 1/2" vertically.

BuckRub · May 6, 2014, 12:04 AM

Shoot another target and then let us see.

higgite · May 6, 2014, 12:35 AM

Was that the first group of the day? The only group of the day? The last group of the day? One odd group among 10 normal groups? You get the picture.

AllenJ · May 6, 2014, 08:51 AM

As you can see from all the posts above there are a number of reasons that this can happen. If it were me, prior to my next range trip, I would check that the scope mount and rings are tight, that the action is tight in the stock, and that the barrel is free floating. I would then go to the range and shoot 3, five shot groups on different targets and keep track on each shot. If the shots string again while the barrel is hot, check to see if it is still free floating.

Jimro · May 6, 2014, 10:13 AM

Quote:

Horizontal groups have causes, horizontal "walking" has other causes. They're not necessarily the same.

I dismissed walking as a cause by the distance between shots in the group pictured. Not that it couldn't be, just that it isn't likely to be, and if the rifle "walked" this grouping wouldn't be unexpected as walking is generally pretty consistent.

Jimro

Brian Pfleuger · May 6, 2014, 10:40 AM

If I had to guess from the information we have, I'd say the far left shot is cold, clean bore.

The rest are only a 1.75" group, vertical dispersion suggests decent ammo, horizontal suggests inconsistent hold, eye position, parallax problem.

JefferS · May 6, 2014, 06:28 PM

Looks like a lot of awesome advice on some things to check out, so I've got some things to do before I report back.

May 5, 2014, 02:24 PM	#3
Jim243 Senior Member Join Date: January 5, 2009 Location: Just off Route 66 Posts: 5,067	The screws are coming loose on your mounts, not the rings but the mounts on the rifle. (most likely the front one) Retighten using some lock-tight. Jim __________________ Si vis pacem, para bellum

May 5, 2014, 04:06 PM	#5
Brian Pfleuger Moderator Emeritus Join Date: June 25, 2008 Location: Austin, CO Posts: 19,578	My first thought is, do you actually KNOW that those shots moved right to left consecutively or is it just an assumption? __________________ Nobody plans to screw up their lives... ...they just don't plan not to. -Andy Stanley

May 5, 2014, 05:25 PM	#6
JefferS Member Join Date: April 27, 2013 Location: Independence, MO Posts: 89	I know the first shot was the left one. I can't guarantee 100% that the rest were moving to the right sequentially, but that was my impression when I finished. I really felt that the last shot was the furthest away from the first because I thought to myself, "Did I pull that much?" I was really only focusing on getting a group at the time and trying to aim at the X consistently, and wasn't keeping track of the individual shots (lesson learned). __________________ *Jeff*

May 5, 2014, 06:36 PM	#7
mikld Senior Member Join Date: February 7, 2009 Location: Southern Oregon! Posts: 2,891	How many of those horizontal groups did you get? __________________ My Anchor is holding fast! I've learned how to stand on my own two knees...

May 5, 2014, 07:28 PM	#9
JefferS Member Join Date: April 27, 2013 Location: Independence, MO Posts: 89	My tea leaves drop right to left. __________________ *Jeff*

May 5, 2014, 02:07 PM	#2
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	I've seen that happen when the (right handed) shooter twists his body clockwise behind the rifle as it rests on something atop a bench. A bit more for each consecutive shot. Is this repeatable? If the rifle is fit and screwed together correctly, I think its a shooter position or rifle holding that's not repeatable from shot to shot. Let someone else shoot it then see what happens.

May 5, 2014, 03:11 PM	#4
eldermike Senior Member Join Date: January 24, 2013 Location: NC Posts: 545	I have had one scope go bad like that, it drove me nuts for a while. I did a new bed job, cast the chamber, even had the crown cut then somone told me to try a different scope....that was it.

May 5, 2014, 07:14 PM	#8
Brian Pfleuger Moderator Emeritus Join Date: June 25, 2008 Location: Austin, CO Posts: 19,578	Without absolute certainty of which shots are which, you'd be better off reading tea leaves.

May 5, 2014, 08:09 PM	#10
Jimro Senior Member Join Date: October 18, 2006 Posts: 7,097	Whether or not the shots impacted in a linear manner is irrelevant to the linear dispersion pattern. The groups indicate that something is shifting. The two most likely culprits have already been identified, shooter position and optic repeatability. Tighten the bases, tighten the rings, move your windage knob a turn around, then a turn back to see if the springs have taken a set or replace the scope with a known good unit. If consistent body position and a new scope don't fix the issue, I would recommend a powder charge change to see what that does, ensuring the barrel is free floated. Jimro __________________ Machine guns are awesome until you have to carry one.

May 5, 2014, 08:31 PM	#11
Brian Pfleuger Moderator Emeritus Join Date: June 25, 2008 Location: Austin, CO Posts: 19,578	Of course it's relevant! If they're not consecutive it could be any number of random reasons. If they are consecutive, it's a single cause (or random chance). Horizontal groups have causes, horizontal "walking" has other causes. They're not necessarily the same.

May 5, 2014, 11:36 PM	#12
Jay24bal Senior Member Join Date: December 13, 2011 Location: Cleveland, OH Posts: 735	Maybe it is too obvious to even ask, but was it windy? I was also out shooting this past weekend in OH, and we had sustained winds in the 20's with gusts into the mid-high 30's. If we call the far left a "flyer" or you pulled it, it is not hard to imagine a 2" group in windy conditions like I had here, especially since you were testing loads and this very well could be a bad load for the gun. I only ask because it was windy as heck here this weekend, and the other four besides the flyer are within 1/2" vertically. __________________ I like guns. Once Fired Brass, Top quality, Fast shipping, Best prices. http://300AacBrass.com/ -10% Coupon use code " Jay24bal "

May 6, 2014, 12:04 AM	#13
BuckRub Junior member Join Date: October 3, 2012 Location: Central Texas Posts: 1,046	Shoot another target and then let us see.

May 6, 2014, 12:35 AM	#14
higgite Senior Member Join Date: October 21, 2010 Posts: 1,025	Was that the first group of the day? The only group of the day? The last group of the day? One odd group among 10 normal groups? You get the picture.

May 6, 2014, 08:51 AM	#15
AllenJ Senior Member Join Date: December 11, 2009 Location: Northern California Posts: 1,766	As you can see from all the posts above there are a number of reasons that this can happen. If it were me, prior to my next range trip, I would check that the scope mount and rings are tight, that the action is tight in the stock, and that the barrel is free floating. I would then go to the range and shoot 3, five shot groups on different targets and keep track on each shot. If the shots string again while the barrel is hot, check to see if it is still free floating.

May 6, 2014, 10:40 AM	#17
Brian Pfleuger Moderator Emeritus Join Date: June 25, 2008 Location: Austin, CO Posts: 19,578	If I had to guess from the information we have, I'd say the far left shot is cold, clean bore. The rest are only a 1.75" group, vertical dispersion suggests decent ammo, horizontal suggests inconsistent hold, eye position, parallax problem. __________________ Nobody plans to screw up their lives... ...they just don't plan not to. -Andy Stanley

May 6, 2014, 06:28 PM	#18
JefferS Member Join Date: April 27, 2013 Location: Independence, MO Posts: 89	Looks like a lot of awesome advice on some things to check out, so I've got some things to do before I report back. __________________ *Jeff*