AR15 inconcistancy

[flyfisherman246]

Over the years I have tried many high quality barrels, receiver, and handguard set ups trying to find an ar15 that shoots like a boltgun. I have built many ar10's that all shoot one little hole and are very predictable and consistent. I just can't seam to get a consistent ar15. It will shoot a 5 shot group at about .5 moa and then the very next group will be 1.5". Or Ill have 3 into a tiny little hole and two flyers that open the group way up. I don't get this problem with the many ar10's I've built. Everything is free floating, lots of handguard/ gasblock room, everything is tight, the gas tube isn't dragging on the bcg.

Currently I am working on two ar15's with bartlein barrels. one is a 16" and the other is 18", both 7 twists. The 18" is built on an aero precision enhanced handguard receiver combo, and the 16" is built on a larue stealth 2.0 receiver set. Both these receiver sets have the handguard mount directly to the receiver not the barrel nut. I have built many ar10's with bartlein barrels and aero enhanced uppers that just stack them every single time.

What am I doing wrong? Where do I look from here?

 

[flyfisherman246]

Here are typical ar10 groups

 

[flyfisherman246]

Then ar15's will shoot a group like this

But then the same load does weird stuff like this

And these groups aren't even that bad. I'll get some flyers that are quite a bit worse. Any ideas?

 

[nn8734]

Not sure the comparison between your large frame and small frame ARs is valid or relevant. Every weapon is different, even if the chambering is the same. Seems like your assembly process was sound (Doesn’t hurt to double check but not the likely cause)

In the case of those AR15 flyers, looks like the pressure curve is different between the shots in the tight group vs the flyers, creating a less symmetrical vibration in your barrel compared to the rounds you’re stacking. So 4 rounds where the load creates an optimal resonant barrel harmonics (ie your “accuracy” node) then the flyer which has either slightly more or less pressure, causing a different vibration away from the node, resulting in the flyer (or an alternate POI for those “flyer” rounds)

Absent any addl. information, I’d check your loads, staring with the brass, making sure shoulder set back is identical, all primers are fitting tight in the pockets. Also check bullet jump, making sure it isn’t widely varying. Thrown charge weights all within .1 grain of your target weight round over round for that recipe.

What is the MV, SD and ES of the AR15 load in the photos?

 

[Back Spin]

OP, looks like your shooting mechanics are in order. Just confirming, the grip and triggers are the same between your AR10’s and 15’s?

Also, do the flyers go laterally as well? Or just vertical spread?

 

[flyfisherman246]

Grips are ergo on all rifles and triggers are all ssa-e's and Larue.

These inconsistencies happen with finely tuned hand loads as well as quality factory ammo. The last picture on the left target is with 77 federal gold medal match. it has 3 into a small cluster and two that are low. I know about the first round/last round flyers, but in this group the last shot wasn't the last round in the mag. Also, I don't get first/last round flyers in my ar10's.

Everyone is always talking about how the ar10's are so difficult to shoot accurately, and the 15's are easier. I have never had a problem getting the ar10's to shoot consistently, but have never had an ar15 that is just predictable.

 

[nn8734]

Grips are ergo on all rifles and triggers are all ssa-e's and Larue.

These inconsistencies happen with finely tuned hand loads as well as quality factory ammo. The last picture on the left target is with 77 federal gold medal match. it has 3 into a small cluster and two that are low. I know about the first round/last round flyers, but in this group the last shot wasn't the last round in the mag. Also, I don't get first/last round flyers in my ar10's.

Everyone is always talking about how the ar10's are so difficult to shoot accurately, and the 15's are easier. I have never had a problem getting the ar10's to shoot consistently, but have never had an ar15 that is just predictable.

I shoot my SR25 well much more consistently than any of my accurized AR15s; that could be a function of me simply shooting the larger platform more often or it could be something else. I also start at 300 yards and work my way to 800 when testing, which mirrors my shooting patterns. Its hard to draw any useful conclusions at 100 yards anyway. So many are wrapped up in evaluating their proficiency, load and rifle performance at 100 yards even though their systems are built to be used at 500+.

I would be interested in knowing if your vertical dispersion, flyers included grows proportionally out to 400 or 500 or if it stays tight relative to increasing distance. For example, if you had 5 shots in a 3" vertical spread or so at 300, then one an inch or two low occasionally, I would consider that a good load. If the flyer is like 6-8" low and it happens one out of every 5 shots, I would be a little concerned. I would not consider horizontal dispersion at this point as that is driven by you or your assessment (or lack thereof) of the wind.

Empirically speaking, how finely tuned are the loads? Again, hard SD/ES numbers would help ground the problem statement and give a place to start. If both factory and your hand loads are producing similar SD/ES and they are low (i.e. low double digits for SD and 2x or less for ES) over at least 5 consecutive shots then at least we know the load(s) are likely not the problem and can rule it out.

Do you have those numbers or no?
If not, I would start collecting that data (5 - 10 shots over Labradar or a good working chronograph), letting it guide your way forward from there.

Perhaps you are sympathetically squeezing the rear bag every so often, slightly altering the POI without realizing it. Perhaps it happens when shooting the smaller, lighter AR15 but not on the heavier AR10 (or if you do, its so slight, it doesn't result in a measurable change in POI, at least at 100.

Assuming those diamonds in the second AR15 picture are 1.25" square, you still are shooting just over 1 MOA (perhaps slightly more) with the flyers which is perfectly fine. Test each loading at 300 yards and see what happens, collecting data as you go. If you are able to put everything, including the flyers into a 4.5" vertical dispersion or better (and only occasionally throw one beyond that which can't be attributable to you) then I would say your rifle is performing well and your loads are good (perhaps the hand load can be tweaked for some marginal improvement getting you under 1 MOA consistently out to your max effective range).

Hope this helps.

 

[JOS]

I get the same symptoms with my LaRue OBR 20". My daughter has the same problem with this gun. I am working with a custom cartridge maker to see if it is my reloads or factory loads. Looking forward to hearing some opinions about this

I was advised to replace the the H2 buffer to H3 and switch the gas port to suppressed. Using 69gr and 77gr bullets. Have yet to get to the range to try this. Like j-huskey said about high bolt speed this might do it.

 

[j-huskey]

You didnt say what the chamber reamer was on the 15's. Curious.

And, just for removing potentials.
a. Remove the gas tube and block.
b. Install another block (w/o tube) turned to block the gas hole.
c. Single load the rounds and hand seat them with the forward assist, gently...

See what happens. If the problem goes away. ......

Adjustable gas block and slow the bolt travel down. If the bolt is slamming forward too hard, it can be resetting the headspace on the cases, and this is one cause (varied headspace) of what u experience.

Best to you, VR,

 

[Constructor]

Are using front end control or just letting the rifle lay on the rest?

 

[bfoosh006]

IMHO... there are so many variables involved, it would be hard to nail a specific cause on your AR.

Clearly you can shoot... so I am going to dismiss that for the most part. ( we all have bad bench days.. but that is easy to notice. )

All the way from "how consistent is your neck tension and release on your reloads" to "how tight a fit on your upper to lower" .. with a bunch of stuff in between.

I have used this article as a guideline for ages... and is better written then I could ever hope to verbally convey.

At the very least, the various AR's I have applied the linked info to... have less fliers, and more consistent groups.
I haven't ever bothered to address "Front/Back Bolt Play".

http://bulletin.accurateshooter.com...-to-build-a-truly-accurate-ar-platform-rifle/