New build won’t group

[Baldness]

I took a new build out today to zero. It is a Sionics 14.8 pinned and welded upper. I put a used eotech exps3 on it. I went to zero it at 36 yards and it was printing 4-5 inch groups more like patterns. I figured the optic might be loose. I checked it and tightened it slightly. It didn’t help, I had another rifle out with me so I took the H2 off that rifle put the eotech on and it grouped fine. So I tried the H2 on the new rifle and same 4 inch groups. It varied both in windage and elevation. I am going to contact Sionics tomorrow and I am sure they will help me. I have talked with them before never had an issue but have heard they’re top notch with customer service. I am just curious if anyone on this forum more knowledgeable than me could shed light on what would cause this. I thought maybe an over torqued barrel nut? Looking forward to any thoughts shared.

[joedirt199]

Who did the pin and weld? Could have over torqued the muzzle device if it is one that has to be clocked for to a certain orientation. Check for any impacts on the muzzle device.

[markm]

I thought maybe an over torqued barrel nut?

I doubt that. I've pulled some Colt nuts off that were installed by Hulk Hogan. Sounds like something Barrel/Ammo related.

[HKGuns]

4-5" groups at 36 yards? That strikes me as impossible if there is any rifling at all in that barrel.

Also, you use the word build and then reference Sionics upper. Which is it?

[556Cliff]

I doubt that. I've pulled some Colt nuts off that were installed by Hulk Hogan. Sounds like something Barrel/Ammo related.

Agree. Unless the barrel nut is loose I don't believe that barrel nut torque has any effect on accuracy.

In this case I'd check for a loose barrel nut. If it's not that, then I'd suspect the pin and weld muzzle device install and the barrel itself.

[La26]

What twist barrel, and what bullet weight? Any sign of the bullet keyholing in target or are the holes perfectly round? Sounds like a barrel that doesn't have a crown, or bullet not matching the barrel twist.

[Baldness]

It’s a Sionics complete upper they did the p&w. I was using green tip and shot the same ammo through my Bcm upper, it did okay. I didn’t think maybe the muzzle device but it makes sense. I never had seen a rifle so all over the place that close.

[lonestardiver]

The twist of the barrel may not be fast enough for that longer bullet.


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[grizzman]

How well did it group with irons?

4” at 36 yards is well beyond a barrel not liking a particular bullet.

My bet is on the optic or mount.

[Baldness]

Barrel is 1-7 and I don’t have irons on it yet. I put two optics on it one was an H2 I’ve had for a couple years now and the eotech did fine on my other rifle