Poor Accuracy - Scope or the Mount?

[GreaseMonkeySRT]

I assembled an AR-15 a couple months ago. Ruger Elite assembled lower, PSA 5.56 1:7 twist 20 inch barreled upper. I mounted a Nikon M-223 mount and M-223 scope on the gun.

First range trip was with 55 grain .223, just to get somewhat of a zero in. Groups at 100 yards kinda sucked, but that's what I would expect.

Second range trip with 75 grain 5.56, and the groups got worse as I shot. I didn't realize like a dolt until after I was out of ammo that my scope mount had loosened off of the rail. When re-tightening, the damn screws stripped out.

Third range trip I have a new scope mount torqued to spec with Loc-Tite applied. I have 75 grain .223 ammo. I get a zero, and while making adjustments I'm getting some wild groups. Three shots would be somewhat close, I'd make 1 or 2 click adjustment right (.5 inch at 100 yards), and the next shot would be 3-4" right. Next grouping would still be pretty sloppy, a couple close and another a few inches off at 100 yards.

My fourth range trip will be today. I took the scope with mount off today, and the screws even with Loc-Tite didn't take much effort to remove. I mounted my EoTech holographic sight on the gun, and I'm going to see how it groups with .223 55 grain ammo. Assuming I have reasonable groups, even though it's not the best ammo choice for the barrel, is there any way to determine if the scope is bad or the mount is bad any other way than swapping parts and seeing what changes? I will say so far I do not like this scope mount. I have the M-308 scope on a Remington 700 with rings and it's a 1 MOA rifle. I have a feeling it's the scope mount, but I'm looking for a potential shortcut to determine that before buying more stuff. I do realize it could be the PSA upper as well, which is why I'm testing it with a different sight today.

Thanks in advance.

[elwarpo]

How are your groups with iron sights (eotechs are not very accurate at 100 yards due to the dot size.)? Could just be the rifle is inaccurate, and nothing to do with the scope/mount.

If you put the rifle in a gun vice, is there any play between the upper and scope? Is there play between the lower and upper? When you over tightened the rings the first time, did you dimple the scope tube? PSA is hit or miss on build quality, is there play between the barrel and upper. Just because the barrel nut is tight, does not mean the barrel has no play in the receiver. Another thing to consider is that 20" barrels put a lot of strain on an upper due to torque/leverage, especially heavy barrels. Most standard uppers will flex and you lose accuracy, that is why accurate AR builds use heavy wall uppers like VLTOR.

PM me for my number if you want to talk.

[dirtmcgirt76239]

definitely see what you can do with irons at 50 or 100 if you have the eyes for it (not that 100 is far but you know what I mean). You should not be doing better with irons so that will tell you something.

[10x25mm]

Which M-223 scope do you have? Is it one of the higher powered models with side parallax adjustment?

Once you are satisfied that you mount is secure, check parallax. Rest the rifle on bags and line it up at a target 100 to 200 yards away. Without touching the rifle, move your head around while looking through the scope. You want to see a full image through the scope, no dark fringes. Does the reticle move on the target as you move your head? You want to try this at both ends of the power range.

If so, you probably need to make a parallax adjustment. Nikon probably has a specific procedure to follow if their side parallax knob does not produce zero parallax at the range indicated on the parallax drum. The usual practice is to set the drum at the range you are using - usually 200 yards - and then loosening the ocular bell and screwing it forward and backward until you achieve zero parallax. This is usually done at maximum power, but the end result needs to be checked across the power range.

If you don't have a parallax problem, you could either have a problem with the upper or something gone wrong inside the scope. Was the 'feel' of the elevation and windage adjustment knobs consistent from click to click? Is the reticle rotating slightly from shot to shot? Does the reticle go off center as you adjust point of impact? These tells of a bad scope are subtle and hard to discern.

[Ol` Joe]

To check your scope shoot a box test.
Fire a 3rd group and give your elevation turret ~12 clicks and fire another group aiming at the exact same place as the 1st group, adjust the horizonal the same amount to the left and shoot again, adjust the elevation 12 clicks down, finally adjust to the right another 12 clicks.
You should be very close with the final group to the spot you placed the original group. If you don't get a pretty good square you may have the scope tilted in the rings or the scope is not tracking. If its a tracking problem send it back to Nikon.


Be aware you need to shoot decent ammo when testing. Wolf, American Eagle, Mil-Surp green tip etc is not going to give you the groups you need or are looking for.

[HemiChallenger]

Ol joe is on to what i was thinking. Tap on the scope after an adjustment and shoot a few more before making another adjustment. I chased a new scope for 40 rnds. Like this once. After it got "loosened up" everything seemed to be ok.

[GreaseMonkeySRT]

Zeroed an EoTech Holographic at 50 yards. I consistently patterned 2 inch groups over 30 rounds fired. Now I know 2 inches at 50 yards isn't all that great, but I was shooting cheap 55 grain .223. I'd expect with slower shooting (I was in a time crunch) and proper match grade ammo with bullet weight for this barrel, under one inch should be no issue.

I ordered an Aero Precision Ultralight scope mount, and I'll re-test again after zero with the box test and go from there.

My M-223 scope is a 3x12, and does have the parallax adjustment. Once it's remounted I'll go through that test as well. The adjustment clicks are consistent, and there doesn't feel like there's any binding or resistance. I never had an issue with my M-308 scope on my Remington 700, but really good rings/base was used for that build. Assuming Nikon's quality is consistent, I'd tend to believe the M-223 base is more of the issue but further diagnosis will tell.

Thanks for the help guys!

[DrScaryGuy]

is there play between the barrel and upper. Just because the barrel nut is tight, does not mean the barrel has no play in the receiver.

This is worth repeating, even if it's not OP's issue.
I was at a store once and looking at a barrel and an upper. I put the barrel in straight, and it rocked back and forth by a degree or two. Not tight at all. I know aluminum can flex and a little play might not be a big issue... but I feel like there is no way a barrel that wobbly could shoot straight.
I should order a receiver lapping tool, but none of the 3 or 4 barrels i've put on since then have been loose.

[partdeux]

My mount wasn't true. Friend made me a hone to run in my drill. Took some polishing compound and slowly cranked down on the screws until I had a good polished clamping surface.

[xtrema312]

I had about the same issue last year. I swapped the scope out and problems went away. Ended up sending back that brand-new scope to Leopold to have it reworked and returned. Set it up again this year and sighted it in without any issues. Erectors had some kind of an issue.