POI Problem with 12" 6mm ARC Build

[lbsand]

 
I finally got the opportunity to take my new Upper build to the range today.
The build consists of:

• Aero Precision M4E1 Threaded Assembled Upper Receiver with the face lapped for squareness.
  
• Toolcraft Bolt Carrier with a properly headspaced San Tan Tactical 6mm ARC Bolt
  
• BCM #4 Charge Handle
  
• ALG 10” EMR V1 Handguard
  
• 12” 6mm ARC Monster Barrel, Odin Works Tunable Gas Block, Aero Nitride Gas Tube and a Silencerco ASR Muzzle Brake calibrated with a sold spacer.
  
• Vortex 1-6x Strike Eagle mounted in a Warne 30mm XSKEL mount.  I’ve used this scope/mount combo many times for initial testing.  The scope was bore-sighted before going to the range.
  
• All parts were brand new except the ALG Handguard.
  

 
The completed Upper assembly was installed on a SBR lower which runs a standard spring and H2 Buffer.  All the uppers used with this Lower Receiver have Adjustable Gas Blocks. 
 
The Problem:

• I decided on a 50-yard suppressed zero with this barrel.  A Silencerco Saker 7.62 suppressor was installed on the Silencerco 7.62 ASR Brake.
  
• I was still shooting approximately 4” high when I ran out of adjustment on the scope.  This has never happened before with this scope or any of my other builds.
  
• I was using factory Hornady 108 gr ELD ammunition that was just chrono'd at 2323 FPS.
  

I'll be completely stripping this Upper early next week.  I'm at a complete loss, so any suggestions/remedies would be greatly appreciated.

Thanks in advance.

[SBRSarge]

Say again.

[lbsand]

Sorry, I'm not sure what you're asking.

[SBRSarge]

All I see on your post are a column of dots aligned at the left of the post.



Ahh! I zoomed in and it shows up as light colored text on an almost matching background.

---

Did you by chance get a scope mount with 20 or 30 moa built into it?

[Lemonaid]

Things you might try: Test without suppressor/brake to eliminate that variable.
Test with a different scope and mount for that variable.
Verify correct barrel nut torque and all torqued components.
If all else fails, Burris makes some rings with inserts that can compensate for misalignment.

[lbsand]

Things you might try:  Test without suppressor/brake to eliminate that variable.
Test with a different scope and mount for that variable.
Verify correct barrel nut torque and all torqued components.
If all else fails, Burris makes some rings with inserts that can compensate for misalignment.

Thank you, Lemonaid.

- Done
- Will try a different scope after disassembly.
- Barrel Nut torque is good.
- Not an option.

Regards

[BluntForceTrauma]

Any progress on this? When you say "I was still shooting approximately 4” high when I ran out of adjustment on the scope," what does that mean? Unless I'm missing something, what it seems to mean is maybe zero out your scope so that your point of impact at your desired zero range becomes the new zero. This is assuming your scope allows you to re-set the zero.

[SBRSarge]

If it has a zero st0p, reset it.

And check your mount to see if it has built in elevation moa. You might have gotten a 20 or 30 moa mount.

[lbsand]

BFT & SBR,
No progress.  The Vortex Strike Eagle 1-6X24 has a total of 140 MOA in Vertical or Horizontal travel and no user-set zero stop.  So, nominally the reticle will shift +/- 70 MOA from the center line of the scope.  The scope's reticle is currently shifted 70 MOA from its center position.  My current point of impact is 4" above my point of aim at 50 yards., or  8 MOA.  There is no travel left in the Elevation turret to move the 8 MOA that I need. 

The scope is installed properly in a Zero MOA mount.  To verify this, I placed  the scope mount base on (2) .500" parallels on a granite surface plate and checked across the top of the scope tube with a .0005" Brown & Sharpe indicator.  The objective side of the tube was .0045" high in 3.875", which, if my math is correct, translates to 4.181 MOA.  I'm going to assume this is probably in tolerance for a Zero MOA Warne mount that retails for $154.

Further more, I've inspected the Silencerco Brake and Suppressor for bullet strikes and there are none.

My next step will be to pull the Handguard and remove the Barrel when I find time.  At that point, I'll verify that the centerline of the Aero Upper Receiver is parallel to the Picatinny Rail.  Since I lapped the Upper Receiver face, I know that it is perpendicular to the Upper Receiver center-line.

Frankly, I can't think of anything left to check, except the barrel.

Regards

[BluntForceTrauma]

I'm trying to visualize your situation. Roll with me on this hypothetical:
1) You set up a target at 50 yards.
2) You put your crosshairs on the center of the bullseye and shoot three rounds.
3) Those three rounds impact, roughly, in a group 4 inches above your point of aim at the bullseye.
4) Are you not able to turn the scope's elevation knob to drop the point of impact four inches so that your next three rounds group on the bullseye at point of aim? If your scope has 1/2 MOA click adjustments, would that be 16 clicks at 100 yards and 8 clicks at 50 yards — if my math is correct?

I'm trying to picture what you're experiencing, but I feel like I'm missing something.

Anything is possible, so if it's a barrel issue I see two possibilities: 1) the bore was drilled incorrectly and off-center within the barrel axis, or 2) maybe the extension was sorta cross-threaded and thus installed at an angle. So let's do the math on those two possibilities:

If you aim at the bullseye at 50 yards and your shots impact 35 inches high cuz the barrel or bore is canted and you thus run out of scope elevation, trigonometry says your bore is at either a 1.146° angle to the barrel axis or your barrel is canted 1.146° relative to the barrel extension. See attached schematic.

   

If it's a barrel issue, I would think your barrel would look like one of the two schematics.

If your barrel doesn't look like that, then it would be simplest to test the point of impact with a different scope altogether or even iron sights. You could also try that Vortex scope on another gun and see if anything's changed.

[SBRSarge]

Hmmm, ya got me stumped!

I like BFT’s ideas. Take off the scope while it is in the mount and try it on another gun, and try a different scope/mount combo on this gun.

And keep us posted, as you work through and solve this we all might get to learn something!

[grayfox]

BFT I’m following everything you wrote, but one thing is backwards I think... 4” at 50 is 8 moa, so 4” adjust at 50 is 16 clicks. At 100, 4” would be the 8 clicks. All 1/2 moa clicks.

[Lemonaid]

When this sort of thing happens in a factory bolt rifle, the culprit is usually the factory base attached to the receiver (the holes drilled and tapped out of alignment for left or right misalignment), or the receiver was formed/milled out of alignment with the bore.
You could try and mount a 20 or 30 moa base backwards to give the scope more down adjustment to start with.
If the axis of the receiver where the barrel shank goes into has an upward tilt, that could explain things.
Check with the receiver level, a level on the scope base and a level near the muzzle and see if there is any cant.

[BluntForceTrauma]

While admitting the theoretical possibility that the barrel could yet have some defect that is escaping analysis, for the reasons shown above in my schematics I don't believe it's the barrel. To impact 35 inches, or more, off point of aim at 50 yards, the defect would have to be obvious.

My current theory is the scope done gave up and broke.

This theory can be tested by mounting the scope on a different gun.

Or, conversely, by mounting a different scope on this gun in question.

[lbsand]

All,
Problem Solved!  I’m anal, a hard head and usually attack most problems the long way.  So, I completely disassembled the Upper and inspected the bore alignment in relation to the Picatinny Rail.  The bore and rail were out of alignment .001” per inch.  Nothing to write home about.  Next, I squared the face a 2nd time to remove the small area of anodizing I generally leave as witness a mark.  The Barrel was reinstalled, a new Barrel Nut was torqued to 45 ft. lbs. and a new 11” Handguard was installed.  Since nothing appeared out of the ordinary, I mounted a 1-5X Burris XTR II scope, instead of the Vortex and headed to the range.  My trusty Strike Eagle done let me down!  I’m now shooting POI @ 50 yards!
Thanks to everyone for the suggestions!
 
Jeff