Author Topic: Receiver and barrel alignment causing elevation sight issues  (Read 1762 times)

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Offline erikc838

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Re: Receiver and barrel alignment causing elevation sight issues
« Reply #15 on: July 14, 2019, 12:28:40 PM »
My HBI 4.25" handguard fits the same way.  The suppressor still fits inside and I am able to zero at 12 yards.  The gun runs so I just don't worry about it.

Offline st381183

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Re: Receiver and barrel alignment causing elevation sight issues
« Reply #16 on: July 15, 2019, 04:09:58 PM »
Well, I went to the range to zero my EVO SBR with the new Pakse handguard and ran into the same problem the OP did.  After bottoming out the CZ OEM front sight I was still super low.  I put the OEM handguard back on and got back to zero.  Very disappointed because this is a neat handguard at a competitive price point.  I’ll contact HBi and see what they say.  At worse I’m out $50 but hopefully HB will suspend sales and see if there is a fix.

Offline HBi

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Re: Receiver and barrel alignment causing elevation sight issues
« Reply #17 on: July 15, 2019, 05:35:14 PM »
We have noticed that (by design) the Evo handguards can be sensitive to barrel nut torque; meaning that if you exceed 10ft*lbs of torque on the barrel nut the handguard itself can begin to deform in compression at the barrel nut interface. Note that the factory barrel nut is not tight with "high torque" but rather "thread locked". The intent is simply to hold the handguard in light compression against the upper receiver. Again, 10ft*lbs is the MOST that should be applied.

The factory pistol handguards seem less susceptible to sight elevation issues due to variance in barrel nut torque because the angle/1913 rail positions the front sight much further away from the barrel nut interface; versus the Sapper handguard where the sight is positioned directly over the barrel nut.

While we have been able to zero all of our test Evo's on factory iron sights without issue, with the variance possible in mating 3-4 large molded parts together like this... like they say anything is possible. We figured we would post a couple basic pictures here to attempt to show typical "squareness" of the Sapper handguards:

This geometry is very important, that the receiver be square to the top 1913 rail:



And of course that the 1913 rail is straight/parallel




The only potential issue that we can find (and maybe what @Rooftop Korean had done earlier in this thread) is that there can be some mold flashing left around this pocket:

Offline HBi

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Re: Receiver and barrel alignment causing elevation sight issues
« Reply #18 on: July 15, 2019, 05:46:36 PM »
Also... speaking on behalf of everyone here at HBI... we here to stand behind our customers 100%. Does not matter where you bought the product or how long you have owned it... we will do everything we can so support our customers. In situations like the ones in this thread we are most concerned with determining the root cause of any issue.

Even if you have modified our parts, we are still interested in knowing the "why" in hopes that we can either improve our products or instructions. I think everyone on this forum has "modified" parts before... that is probably why we are all here  ;)

Please never hesitate to call/email/message us with any questions or if you need any help with install or want pictures, measurements, additional info, etc...

Offline st381183

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Re: Receiver and barrel alignment causing elevation sight issues
« Reply #19 on: July 15, 2019, 06:17:20 PM »
I installed per instructions, hand tight plus 1/8” turn and encountered the issue where I cannot zero the gun.  I really like the handguard but it seems way to sensitive to instructed or even minor overtightening.  I didn’t use a torque wrench but I can tell you I did exactly as the directions stated because I was afraid of overtightening going into this project having removed my factory handguard in the past.  It looks good and is priced right but some tweaking to strengthen it for regular installation may be needed. I also found the bottom Mlok to be out of spec as well but didn’t modify it. 

What I am confident in is that HBi will make things right by its customers.  Maybe an aluminum one is in my future because I really liked the looks of the Pakse.

Offline mikeinak

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Re: Receiver and barrel alignment causing elevation sight issues
« Reply #20 on: July 15, 2019, 06:39:15 PM »
Just checked mine on a glass table and it's even.Took it out on the weekend and it was pretty close to zeroed also.

Offline st381183

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Re: Receiver and barrel alignment causing elevation sight issues
« Reply #21 on: July 15, 2019, 08:44:11 PM »
"The factory pistol handguards seem less susceptible to sight elevation issues due to variance in barrel nut torque because the angle/1913 rail positions the front sight much further away from the barrel nut interface;"

That explains why CZ angled the front of the factory handguard.

Offline Rooftop Korean

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Re: Receiver and barrel alignment causing elevation sight issues
« Reply #22 on: July 15, 2019, 11:39:30 PM »
I installed my Paske Hand guard per the manual.  The method I used was to hand tighten then go an additional 1/8 turn every time.  So far I've done this procedure about four times for troubleshooting and fitting the hand guard to the receiver.  I basically shaved the back end of the hand guard at a very shallow angle.  I fitted the hand guard to the receiver per the manual and checked the flatness of the hand guards picatinny rail to the receiver's picatinny rail.  When I finally got it flat I figure the angle I shaved off is about 1.5*.  In other words the picatinny rail is 1/16" shorter and the bottom of the hand guard is the same original length. 

I took it to the range today and this is the result with Magpul Mbus Pro sights.  The front sight is still at it's maximum setting but it's much better than it was.  I'm sure if I used the Original Scorpion sights then point of aim / point of impact would be the same.

@ 50'

I then put the C-More RDS back on and placed the Mbus Pro rear sight in front of the Red dot sight.  I aimed for the head and the grouping was decent with my novice shooting skills. 

@ 50'

Thank you HBi for your interest in this thread.  I didn't want to contact you guys until I fully understood what was going and a range report.  I hope my experience helps you and anyone else out there.
« Last Edit: July 16, 2019, 12:04:54 AM by Rooftop Korean »

Offline kb377

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Re: Receiver and barrel alignment causing elevation sight issues
« Reply #23 on: July 15, 2019, 11:50:36 PM »
I had emailed HBI this weekend with a heads up to the issues and got a reply earlier today, then saw their response here also. I really appreciate their help and responsiveness.

I just went and checked the Pakse handguard (it's off the gun) with a straight edge, and both the rail and the rear edge that interfaces against the receiver were both straight. When I originally installed the Sapper, I tightened the barrel nut finger-tight snug against the handguard, then added 1/8 turn or so with the wrench.

I had reinstalled the factory handguard, so I placed the straight edge along the top rail on it and discovered it has a slight downward slant also (although not nearly as pronounced as the Pakse).

Not sure if the issue is the handguard being highly sensitive to barrel nut torque or if the front edge of the receiver isn't plumb. 

Offline st381183

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Re: Receiver and barrel alignment causing elevation sight issues
« Reply #24 on: July 16, 2019, 12:02:32 AM »
I had emailed HBI this weekend with a heads up to the issues and got a reply earlier today, then saw their response here also. I really appreciate their help and responsiveness.

I just went and checked the Pakse handguard (it's off the gun) with a straight edge, and both the rail and the rear edge that interfaces against the receiver were both straight. When I originally installed the Sapper, I tightened the barrel nut finger-tight snug against the handguard, then added 1/8 turn or so with the wrench.

I had reinstalled the factory handguard, so I placed the straight edge along the top rail on it and discovered it has a slight downward slant also (although not nearly as pronounced as the Pakse).

Not sure if the issue is the handguard being highly sensitive to barrel nut torque or if the front edge of the receiver isn't plumb.

I’m running a barrel cooler on my EVO so the barrel nut tightens against the plastic washer, then the hand guard, and then against the cooler so there is more support there than just the nut against the Pakse hand guard.  If the hand guards are that sensitive to barrel nut torque then they are going to be continually problematic.  I wonder if the aluminum hand guards are better at controlling rigidity during barrel nut tightening.

Offline kb377

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Re: Receiver and barrel alignment causing elevation sight issues
« Reply #25 on: July 17, 2019, 05:36:40 PM »
I pulled mine apart again today to investigate further.

After disassembly, I mounted the receiver in a vise and used a small bubble level to ensure the top rail  was level. I slid both the factory and Pakse handguards onto the gun and held them flat against the receiver face...both were straight according to the bubble level.

Then I figured out the issue...using the level on the barrel, I discovered mine has a slight downward cant in relation to the receiver. Before installing the barrel nut, the handguard indexes off the front of the receiver and is level. Once the barrel nut is installed and tightened, it pulls the front of the handguard downward. I may try and relieve some material from the channel the barrel nut resides in to see if that will allow the handguard to angle up ever so slightly.

Offline Rooftop Korean

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Re: Receiver and barrel alignment causing elevation sight issues
« Reply #26 on: July 17, 2019, 07:11:44 PM »
I also found that the barrel is canted down enough to cause aiming issues.  Sanding down the receiver end of the hand guard at an angle fixed this for me.  The risk here is removing too much material or uneven shaping of hand guard.  It is working well for me. 

Offline kb377

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Re: Receiver and barrel alignment causing elevation sight issues
« Reply #27 on: July 17, 2019, 09:57:38 PM »
I tried sanding, but each time I reinstalled the barrel nut it pulled the front of the handguard back down.

I don't really use the iron sights that much...I'll just live with the issue until the HBI FDE aluminum handguards come back in stock.

Offline erikc838

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Re: Receiver and barrel alignment causing elevation sight issues
« Reply #28 on: July 19, 2019, 09:29:06 AM »
They can have the same issue.
« Last Edit: July 19, 2019, 12:58:05 PM by erikc838 »

Offline dcompton

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Re: Receiver and barrel alignment causing elevation sight issues
« Reply #29 on: July 22, 2019, 02:17:25 PM »
I’m having the same problem. My barre is canted downward. Have tried Sapper and Manticore transformer with same results. I completely disassembled today and it looks like with just the barrel in the receiver it is canted WAY down. It’s like the front of the receiver at the trunnion lugs isn’t square. I have no clue how to go about fixing this.