Group POI Shift?

Str8Shooter

Str8Shooter

Member
During my last few range outings I've noticed that the POI on my AR has been shifting a bit. The first string of 5 at 200 yds is about 2" low and a little spread out... about 3", then the second string is right on the money and less than 2" for 5 shots. I've been thinking about lapping the upper to see if this helps. Any other suggestions would be appreciated.
 
A warm barrel will do that.

It takes me a week to zero a hunting rifle, I will bore sight it, then put several rounds on paper and make the adjustments to get it centered @100yds. As it warms up, the groups will get tighter and tighter.

The following day I will fire a single cold bore shot and adjust the scope accordingly.
I will then continue the process of once a day cold bore shots until it hits dead center every day of the week right out of the bag........call me anal, but shot groups don't impress me much, dead coyotes on a cold morning do.
 
Originally Posted By: Zen ArcheryToo many variables not accounted for from shooter to equipment that it would be hard to determine.

Scope mounts are properly torqued and solid... scope is reliable from use on other rifles...
 
Chryo treatment could help, it relieves internal metal stress. A friend had a custom rifle built and it would walk up to 3" as it warmed, the chryo solved the problem. My father had a perfectly good shooting at that was right around the 1moa mark sent in, it is now around a 1/2moa rifle. They both went to 300below
 
Originally Posted By: 204 ARWhat rifle set-up? ff tube?

16" BHW M4 contour, 1x8 twist, 5.56 cal., Midwest Industries Gen 2 SS Free float handguard... Rock River lower/ Andersen upper receiver
 
Is the scope STILL reliable? I would maybe re-mount it on another gun and check. If you have good rings and everything is torqued properly then you shouldnt have an issue (this includes the barrel nuts etc if you built it yourself)
 
You shouldn't need to lap an AR receiver if the receiver is in spec and from a reputable manufacturer. If you have ensured your scope mount is properly torqued I would suspect the barrel isn't torqued properly. All of this is assuming you are using proper shooting techniques from a solid rest and pressure is not being exerted upon the barrel while firing.
 
Originally Posted By: NightvisionaryYou shouldn't need to lap an AR receiver if the receiver is in spec and from a reputable manufacturer. If you have ensured your scope mount is properly torqued I would suspect the barrel isn't torqued properly. All of this is assuming you are using proper shooting techniques from a solid rest and pressure is not being exerted upon the barrel while firing.

I was wondering about the barrel torque... I couldn't get to the next slot for the gas tube on the barrel nut, so I had to go back one notch. It seemed like I might have been a little light on the torque.
 
Originally Posted By: Arizona BushmanA warm barrel will do that.

It takes me a week to zero a hunting rifle, I will bore sight it, then put several rounds on paper and make the adjustments to get it centered @100yds. As it warms up, the groups will get tighter and tighter.

The following day I will fire a single cold bore shot and adjust the scope accordingly.
I will then continue the process of once a day cold bore shots until it hits dead center every day of the week right out of the bag........call me anal, but shot groups don't impress me much, dead coyotes on a cold morning do.

IIRC, that's very similar to the way Carlos Hathcock sighted in his sniper rifles.
The COLD BORE shot is the most important to me. But, nice tight groups are lots of fun too.
 
If the weapon or barrel will not put ALL shots in the same hole 1-5 then I don't own it. Life is too short to shoot crap.

Most of the time it is the shooter that is the problem not the weapon. The shooter gets a little ancy to finish up the group and looses concentration. Hence all the threads about a 5 shot group with a flyer on fifth shot. We have them shoot a 8 shot group and then on the 8th shot they get the flyer.

A lot of times it comes down to mechanics of shooting consistently through every shot.
One shot a day is easy when you just have to focus on one shot.
Good thing about that is your still getting it zeroed in. Problem is it just takes days instead of minutes.

Have a buddy shoot a string and see what happens to your group to see if it is you or the weapon.
 
Originally Posted By: Str8ShooterOriginally Posted By: NightvisionaryYou shouldn't need to lap an AR receiver if the receiver is in spec and from a reputable manufacturer. If you have ensured your scope mount is properly torqued I would suspect the barrel isn't torqued properly. All of this is assuming you are using proper shooting techniques from a solid rest and pressure is not being exerted upon the barrel while firing.

I was wondering about the barrel torque... I couldn't get to the next slot for the gas tube on the barrel nut, so I had to go back one notch. It seemed like I might have been a little light on the torque.

If you are light on torque you must go to the next. You can lap your receiver to remove some material to make it easier to get to the next slot also.

I have one that I put on that I thought was going to bust but I put it in the vise using the rail clamping devise and got busy. You can do it with the right tools.
 
I pulled the gun apart last night and I'm pretty sure that I found the issue. The barrel nut took very little effort to loosen, definitely not torqued down properly. I'm going to lap the upper receiver, torque it down good, and try shooting it again.
 
Uncle had a colt AR that had the same symptoms. It was a loose barrel nut. Lap it if you want but I think if you get the nut tightened down properly you will be happy!
 
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Problem 1) Heat distortion on the barrel....Problem 2) Mental fatigue from concentrating on any individual group...I have found in the past that when I am watching each shot in any group, I will throw one, or more, out due to losing concentration on the initial point of aim...

I perform much better when I forget the point of impacts and just focus on my sight picture, then my groups tend to be tight...

If you fired more shots than three in reasonably fast time, anything less that a bull barrel will distort to some degree...The longer the distance, the more pronounced the distortion...
 


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