Cinders

Hundie

Solved! Thanks for the help and advice, everyone! I was getting a weird pattern before: firing at one point, I would get 2 distinct, tight groups split by several inches. After taking it apart, we figured that the barrel and comp were torqued correctly, the gas tube was correct and not rubbing, and the shroud was not rubbing either. The scope mount was very tight and torqued to specs. It appears to have been this rubbing issue with the scope touching the shroud railing. I moved it back a lug to be fully on the upper receiver and the problem seems to have gone away. Note: not a split group in picture, that was me dialing the scope in on 2 different groupings.

I'm contemplating doing a single pass with a file across those 2 friction points on the scope mount. I can't see anything positive coming out of the 2 contact points. Plus it rubs down the metal

Ok, I suck at quoting. Trying to quote 98Z to get your attention. See post previous to this one! Sorry for confusion.

Sorry for the delay, been stuck on non-stop 24 hour shifts due to holidays and staffing (thanks corrupt politicians for ignoring major city problems!) Thanks for the replies thus far. I should be headed to the range this coming week to test if the rubbing was the issue. Attached is a distant photo. Note: I moved the scope mount back 1 lug, this is after I saw the rubbing. Originally, the front of the scope mount was on the first shroud lug (bridging the shroud and the upper). I emailed American Defense and got a lackluster reply that repeated what I had said the problem was. I asked them if I have the mount backwards or why does the scope mount have 2 weird points of contact. Response: "Thank you for contacting us. It looks like the rail may be shifting under recoil or the rail lugs are taller than normal and are rubbing on high spots on the rail."

Not sure what you mean on pushed forward. The front scope mount was on the first notch of the shroud rail and the 2nd mounting point was on the main body of the AR rail. I'm seeing that metal rubbing (sorry for blurry pic) on the shroud rail where the scope mount was touching it. I do suspect movement as well, but the question is why and what to do about it. Questions: 1) Should the shroud rail be moving like that to cause that rubbing? 2) Should the scope mount be touching the rail like that? 3) Moving the scope mount to be completely on the AR upper rail is a good solution? Or should I look at returning the mount or modifying it? Thanks for any advice?

While trying to track down a strange inaccuracy issue where I'd get a tight 3 round group in one spot and then a tight 2 round group 2 inches over to the right (rinse and repeat every grouping), I came across rub marks where the scope mount is rubbing, possibly the cause of the issue. The scope mount in the picture isn't where it was before, I had the scope mount 1 notch forward so it bridge onto the first notch of the shroud. After noticing the rubbing, I moved the mount back a notch to see if that fixed the problem (haven't been able to go shooting yet), but I can see the 2 points of contact again (2nd picture). Can I get some advice on this? Do I have the scope mount backwards? Should I file it down to fix the rub points? Am I doing something wrong here? Thanks!

Thanks, 98Z! Yeah, Dust, that looks pretty similar. Mine are split a little more, but very tight groups in 2 distinct places, rather than a looser grouping.

Thanks for linking that! Yeah, I tried a better scope with a different mount and the grouping got a little worse but with the same pattern (2 tight groups left and right of the aim point). I did read your gas block reference, Rex, and I'm wondering if I can just run it by a real expert who can give me a more definite answer. It is a process to get to a range (and find ammo), so I'm not so keen on slowly trying out a scope swap, removing compensator, re-torque barrel, taking apart gas block to see if I can figure out if it was touching something. Also, good question: which gunsmith? I'm asking is if this is even a thing to approach a gunsmith about.

Hi all! I'm still at it with my .308, trying to figure out a weird split pattern I'm getting. Had to take a break during the Great Ammo Shortage of 'ought 20. Also just found out my Timney trigger is defective 😞 So working on replacing that. I'm getting a little fed up trying to find the problem with my rifle, it's a slow process of trying to borrow parts or to get to the range (or get ammo). Would a gunsmith be able to diagnose my rifle? It could be the barrel, the gas block, the compensator (swapped scope/mount out, roughly the same split pattern as before). Thanks!

I'll get a pic up. We used his AR-15 vice block to torque it to specs (the barrel). It is free floating except for the heavy duty compensator on the front. Should I look at taking off the compensator to test? It's on there right and tight with shims, according to specs. Thanks for advice so far. I'll try some more groups with pics to help you all help me, lol. I can recall seeing this *once* before like 15 years ago in the service. I don't know what the real problem was, but they sent the rifle in to be re-barreled and it came back working fine. The theory was the barrel fiberglass bedding was compromised, but nobody that really confirmed that. Last question: I think this is purely a barrel issue, does that compute? The compensator is unlikely to produce this randomness. I'll try re-torquing the barrel nut and test again.

That's what throws us! Only to point out some credibility for the human side of the gun, both my friend and I were Marine snipers (amazingly ran into each other again at the same job years later). Now, having said that, I was used to everything being provided by gun-savvy people. But I'm very good with parallax, stock weld, scope relief, etc. We tested the parallax down to the smallest change, have steady breath holds, slow trigger squeeze. My friend has stayed in the gun community and builds AR-15s while I'm coming back to the community after a long break. I'm going to borrow his scope and mount again. I used his for the break-in and got groups about 2.5 MOA at 100yds. Got my new scope and mount and suddenly I'm seeing ~1 MOA groups. If I shot 5 rounds, I'd see a 3-group touching and a 2-group touching, separated by an inch or so. He produced the same thing. We both had a flyer every 10 rounds or so. Just enough to make us question if it is us or the rifle is quirky.

Timney trigger Aero Precision upper and lower and handguard Zero Fail BCG Vortex Diamondback 4-16X scope American Defense Recon straight scope mounts (tightened to 18 inch-pounds) (this model has 2X quick release lock downs) My only 2 guesses are: 1) The gun is not accurate and these are simply part of the cone of fire. They just look like there is a tight pattern but are random. 2) The scope is moving, despite very tight brackets and no discernible movement upon physical inspection.

Hi all! Wasn't sure what sub-forum this belonged in, but I could use a pointer in the right direction to figure this problem out: Criterion 18" M118 hybrid Precision Arms M11 muzzle brake built a new AR308, trying different ammunition in it, and the one consistent thing that I'm getting is tight, separate groupings. Plus a few flyers about every 5 rounds. This was with Hornady Match grade 168 gr. (Lower grade ammo produced exactly the same results just with more flyers and a looser group). In effect, if I adjust my crosshair to center the separate groups, I'd have 3 round tight group to the left of the crosshair and a 3 round tight group to the right of the crosshair and a few flyers. My friend shot this rifle and got similar results. Tight groups that won't stay in one place. Is this just inaccuracy of the rifle showing random patterns? Shoot a 20 round group and look for an average? I did the scope mount to specs, but tighten it more?

Solved! The Armalite buffer and spring fixed the problem. I am having about 3 out of 10 rounds getting "bit" as the bolt face hits the casing. Borrowed a slightly softer buffer spring and that seemed to fix the problem. Thanks again everyone! It was just a balance of gas vs buffer issue.