Side to side groups

tj66

New member
Working on a 6x6.8 for a friend. It's 22" 10 twist Xcaliber. It shoots right around .5 5 shot groups... Problem is it shoots 2 seperate groups in 10 rounds. Every other shot goes about 1" horizontally back and forth. Giving us 2 .5" clusters. About to drive us nuts. Changed scope out with same results.

Any ideas?
 
1" is a lot. Assuming it's not shooter error, or the front/rear rest, or the optics...

My first guess would be a poor fitting upper/lower. That would explain it perfectly. Even if it "feels" snug, it may not be snug enough. Maybe it's just the pins causing a little tiny bit of play. This could easily cause the upper to drift a tiny bit between shots independent of the lower no matter how steady the lower is held.

Check the gas tube alignment, make sure it is free floated through the handguard and is propperly aligned with your bolt.
 
If your shooting handloads try changing the COL a bit. Load 5 a bit (.05) longer and 5 (.05) a bit shorter. Then proceed in direction of improvement in .02 increments plus and minus.
 
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I have a build that I used a brand of handguard that required 75 ft lbs of barrel nut torque. When torqued that tight the nut made slight contact with the upper receiver(didn't catch) 2 things happened 1. Barrel nut torque was not actually achieved so group's would walk 2. Barrel would loosen very slowly, groups would start open up.
To me I would check nut/gas tube clearance, barrel nut fitment/torque. I have seen the cross bolt of a picatinny ring get stretched and this will cause a left right left right poi. Usually a front stretched cross bolt group's will move left slowly as the bolt losses thread stretch.
 
Try using only 1 side of the mag for a group. Load it up, but only shoot every other round and see what happens. If that turns out good, try the other side of the mag.
 
I had a similar problem to yours.

The cure was to read the scope rings mfgrs directions.
I was used to tighteningr rings kinda like your would tighten a tire lug nuts, kinda move around, opposites and work around the horn.

The fix was to tighten the rings the way the mfgr said

The ring halves clamped on a vertical post. I did not tighten the bottom cap screws first, then the top screws.

When you tighten the top screws too much the bottom screws can not tighten thering havles to the bottom post so the screws can be tight but the scope can walk side to side.

After I traded off the new scope , saw the shiney spots on the bottom clamping screws, I cussed, installed ther poorer used scope I trades for.

Now the rifle shoots extremely well, only difference is I tightend the scope rings according to mfgrs instructions




ap screw
 
Got it shooting good now. I tore it down and didn't really find anything screaming at me other than the barrel nut was really tight. Don't know if that was stressing the receiver or not. Swapped the receiver for a spare I had, torqued nut to 50 lbs and now its shooting 1/2-3/4" round groups. Don't know what brand the old one was, as he bought the complete upper used. I thought for sure I would find something just a touch loose somewhere.

Thanks for all of the help/suggestions.
 
tj, if you run into any further issues, or maybe go back to the other receiver, think about shimming the barrel in the receiver as well. You would be surprised how much shim will go into that joint sometimes. Tightens things up nicely.
 
Originally Posted By: 204 ARTry using only 1 side of the mag for a group. Load it up, but only shoot every other round and see what happens. If that turns out good, try the other side of the mag.


Not being an AR guy I have a question. Before I ask, I have had AR's and had a RRA that was as accurate as most bolt rifles. They just aren't my cup o tea.

So you load your mag, the bolt comes by and picks up a round and shoves it into the chamber, then the bolt locks up, you pull the trigger and BOOM. Does it really make a difference which side of the mag the bullet was on? Seriously, this is a for real question cause I don't know. I would never have thought that would make a difference.
 
Originally Posted By: baitpiletj, if you run into any further issues, or maybe go back to the other receiver, think about shimming the barrel in the receiver as well. You would be surprised how much shim will go into that joint sometimes. Tightens things up nicely.

I will check that out also. I'm guessing this is why the upper was for sale. Bud is happy now... That's all that really matters. I've got another barrel I can mount up for entertainment one of these days.
 
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Originally Posted By: pyscodogOriginally Posted By: 204 ARTry using only 1 side of the mag for a group. Load it up, but only shoot every other round and see what happens. If that turns out good, try the other side of the mag.


Not being an AR guy I have a question. Before I ask, I have had AR's and had a RRA that was as accurate as most bolt rifles. They just aren't my cup o tea.

So you load your mag, the bolt comes by and picks up a round and shoves it into the chamber, then the bolt locks up, you pull the trigger and BOOM. Does it really make a difference which side of the mag the bullet was on? Seriously, this is a for real question cause I don't know. I would never have thought that would make a difference.

I've heard of this before also. I think it had to do with brass sizing issues or how they ended up chambering. Been awhile so I don't remember what it was
 
Originally Posted By: pyscodogOriginally Posted By: 204 ARTry using only 1 side of the mag for a group. Load it up, but only shoot every other round and see what happens. If that turns out good, try the other side of the mag.


Not being an AR guy I have a question. Before I ask, I have had AR's and had a RRA that was as accurate as most bolt rifles. They just aren't my cup o tea.

So you load your mag, the bolt comes by and picks up a round and shoves it into the chamber, then the bolt locks up, you pull the trigger and BOOM. Does it really make a difference which side of the mag the bullet was on? Seriously, this is a for real question cause I don't know. I would never have thought that would make a difference.

It's never happened to me, that I've noticed anyway. I've read about it somewhere, and am repeating it as it seemed like the perfect explanation for what was happening here. But if you think about it, on a double stack mag for a semiauto, you're using two different feed ramps and going it the chamber at two different angles. If one side was messed up for some reason it could cause some damage to the rounds coming from that side. And testing it is simple enough to be worth trying and eliminating one possible cause.

It sounds like the op got his issues figured out, good on him for the troubleshooting.
 
I understand what your saying. I wish the OP hadn't got his rifle figures out until he tried your idea. LOL, just kidding. Glad he got it working!
 
Real nice thread with a happy ending.

For anybody passing through at a later date, one of my rifles would not line up until 82 ft lbs of torque.

I was very worried about this being too tight 4-5 years ago.

LoL! It is one of my most accurate rifles to this day. And the one i shoot the most.
 
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