I am considering rebarreling a rifle due to less than desired accuracy. The rifle (AR-15) has a SS 16" HBAR barrel and has been shooting 5 shot 100yd groups from a solid sandbag rest of about 1.5 MOA with several handloads. I believe the rifle should do better so I am considering rebarreling it with a more expensive match type barrel as I really want 1 MOA or less for a 200 yard coyote gun. When I took the scope off to take the upper to the gunsmith for the rebarreling I found that the eyepiece lock ring had loosened (it was about 1/2 turn loose) and the eyepiece could be slightly wobbled. It was not floppy loose, just enough that you could get about 1/32" wiggle to it if you moved it side to side but not by just tipping the scope around.

I understand that the lock ring is to set the focus of the eyepiece so it stays put. Would this bit of looseness cause an accuracy problem or just focus issue? My options are to go back and shoot groups all over again or get it rebarreled and move on. I suspect that there was not that much movement of the eyepiece and I'm obsessing over nothing. With my bolt gun (.223) I can easily keep it inside 1/2 MOA so I don't think the crappy accuracy was me. I have already bought the new barrel. Anybody else have a loose lock ring?

I doubt it's the lock ring.
What bullet?
What twist?
What powder?

With a 16" Hbar, if it's not shot out it should do better. You could mount a scope you know is good and try again.
You could have someone else try it and see if they have the same results.
Sometimes it's the nut behind the trigger.

Redfield 2X7X33 Accurange scope on 7X

53gr HP Sierra match 27gr H335
60gr V-max 25gr H335
60gr SP Hornady 26gr W748
The above loads were worked up by using at least 2 or 3 other charges of powder for each load.

1:9 twist, trigger job (smoothed).

It certainly could be the barrel if you've eliminated the other factors.
I usually load more than two or three charge weights to find my accuracy nodes. I will usually load 5-7 charge weights in .2 gr increments to find the sweet spot.
But even those off the node should do better than 1.5 moa with a good barrel.

So, you figure the loose scope eyepiece wasn't the reason for the open groups?

Unless the eyepiece is very loose, no.
Most of my scopes the eyepiece is quite stiff and the lock ring is just insurance.
My newer scopes don't even have lock rings.

I just figured that since I could wiggle the eyepiece that it might have opened up my groups. I guess I'm getting a new barrel. Thanks for the input.

What did you buy for the new barrel?

Bear Creek arsenal: AR-15 Barrel: 18" Heavy Barrel, W/ 1-9 Twist, .223 Wylde, Parkerized Finish

Cobra Tactical Systems: 16" H-Bar Carbine Barrel Wylde Nitride 1:9 | 5.56/.223 - Melonite 16" ~$95 shipped

I was told that Bear Cr barrels would easily shoot 1 MOA so I ordered one and then found Cobra Systems who guaranteed 1/2 MOA on their barrels. ~$128 shipped

Good luck!

What's the scope?

Redfield Revolution 2X7X33mm Accu-Range reticle using the 7X powder for the target work