Brand new Picatinny riser rail causes rifle to shoot 3 MOA to the right

[JimGnitecki]

See post #5.......

End of thread

No, not quite end of thread: Despite the awful weather we have been having (rain, snow, fog, and very cold temperatures!) I managed to get to the range this morning. This was the first range session since I replaced the TruGlo riser with the Wheeler riser.

Recall that the TruGlo had shifted the POI to the right by 3 MOA. I was delighted to see this morning that after replacing the TruGlo riser with the Wheeler riser, and rezeroing, the windage adjustment on the scope returned to pretty much exactly where it had been before I installed the TruGlo, which was at the zero factory windage setting for the scope.

Unless this is a wild coincidence, I think this proves that the TruGlo was machined just a tiny bit "off" of being parallel to the barrel when mounted.

Jim G

 

[rabid wombat]

Unless this is a wild coincidence,

Let me see if I got this…when the scope was mounted in the rings, and the rings were mounted to the bases, which were mounted to the rifle…the rounds impacted where the horizontal was in line with expectations, and the vertical was off, but could be adjusted to zero - did I get this right?

Then…when the scope was mounted in the rings, and the rings were mounted to the riser, and the riser was mounted to the bases, which were mounted to the rifle…the rounds impacted were off the horizontal expectations, and the vertical was off, but both could be adjusted to zero - did I get this right?

Finally…when the scope was mounted in the rings, and the rings were mounted to the NEW riser, and the riser was mounted to the bases, which were mounted to the rifle…the rounds impacted where the horizontal was in line with expectations, but the vertical was off, but could be adjusted to zero - did I get this right?

Dumb luck….

Let’s think about the variables:

• Bore true to the action
• Action mounting location/surface true to the action and true to the bore
• Mounting screw holes true to the above
• Mounting screws true
• Torque consistent
• Bases - the same
• Rings - the same
• Scope was centered horizontally and vertically coming from the factory - did you count the clicks end to end to make sure it was centered?
• Etc.

Let’s play with the scope…on horizontally, but off vertically from the factory. If the scope reticle was perfectly centered leaving the factory, the balance of the system was off vertically. If the scope reticle was coincidently off horizontally from the factory but aligned with the system, the system was fine, but the scope was off. Three minutes in the system you describe is nothing. The whole point of adjustments is to account for all the imperfect interfaces. Welcome to tolerance stack up. Like wind, some dial in, some dial out…

 

[rabid wombat]

For the Engineers…

https://www.thomasmechanicaldesign.com/the-mitch-blog/picatinny-and-nato-rails-gdt

 

[Grumpy_old_Fart]

did anyone comment about what type of screws retain the rail? Are they shouldered screws? If so, the hole tolerance in the rail could be off allowing the whopping 3 moa shift.
Does anyone make a rail with tapered shoulder screws and chamfered holes to help center the rail?
I haven't seen one, but they might exist.

Eta: tolerance stack is a thing. Perfect manufacturing is not.

 

[Show Me]

Sorry. I don't know the proper terminology. What I mean to say is that the riser rail and the rifle barrel were both perfectly PARALLEL withOUT requiring any scope windage correction, before the riser was added, and should have remained perfectly parallel or pretty darn close to perfectly, if a proper CNC machining process was used to make the riser rail.

Jim G

"Proper CNC process" your not sounding so good.

 

[JimGnitecki]

did anyone comment about what type of screws retain the rail? Are they shouldered screws? If so, the hole tolerance in the rail could be off allowing the whopping 3 moa shift.
Does anyone make a rail with tapered shoulder screws and chamfered holes to help center the rail?
I haven't seen one, but they might exist.

Eta: tolerance stack is a thing. Perfect manufacturing is not.

No, both the TruGlo and the Wheeler rails use a design that squeezes either 1 (TruGlo) or 3 (Wheeler) movable plate sections against the rail to secure it in place on their mating surface. So any hole size tolerance has zero effect on the accuracy of alignment.

And there is no opportunity for tolerance stacking in this approach.

Jim G

 

[JimGnitecki]

"Proper CNC process" your not sounding so good.

Oh really? It might not be the expression YOU use, but it is not incorrect, and it saves words.

A proper CNC process is one in which:
- The CNC machine being used is not worn beyond normal CNC tolerances
- The CNC machine being used has been properly programmed
- The CNC machine being used has been properly set up for the operation

Jim G

 

[Show Me]

Well that just proves the Chinese children on their second shift of the day were a few thousands off . also proves paint ball quality isn't fire arm quality. Instead of stacking tolerances a proper set of scope rings would be good. Thanks for the first year CNC lesson. I'll pass it on to the next apprentice.

 

[JimGnitecki]

Well that just proves the Chinese children on their second shift of the day were a few thousands off . also proves paint ball quality isn't fire arm quality. Instead of stacking tolerances a proper set of scope rings would be good. Thanks for the first year CNC lesson. I'll pass it on to the next apprentice.

I am not sure that a "proper set of scope rings" would provide closer tolerance. I think maybe a one-piece mount provides closer tolerance control because any actual error in either position or angle is spread over a much longer distance than the very short distances in each scope ring. AND the one piece mount is far more rigid which prevents torsional stresses that add to the potential for error. The best scope rings try to address this torsional stresses issue by machining both of the rings in one pair to be sold together in ONE operation TOGETHER, which at least reduces the potential for torsional stresses, but does not eliminate it (since the clamping rail on each scope has its OWN angular and posiitonal tolerance).

Jim G

 

[Show Me]

I am not sure that a "proper set of scope rings" would provide closer tolerance. I think maybe a one-piece mount provides closer tolerance control because any actual error in either position or angle is spread over a much longer distance than the very short distances in each scope ring. AND the one piece mount is far more rigid which prevents torsional stresses that add to the potential for error. The best scope rings try to address this torsional stresses issue by machining both of the rings in one pair to be sold together in ONE operation TOGETHER, which at least reduces the potential for torsional stresses, but does not eliminate it (since the clamping rail on each scope has its OWN angular and posiitonal tolerance).

Jim G

so what's with the cheep rails

 

[Grumpy_old_Fart]

No, both the TruGlo and the Wheeler rails use a design that squeezes either 1 (TruGlo) or 3 (Wheeler) movable plate sections against the rail to secure it in place on their mating surface. So any hole size tolerance has zero effect on the accuracy of alignment.

And there is no opportunity for tolerance stacking in this approach.

Jim G

I meant the screws that attach the rail to the receiver.

To prove my point, remove the optic, loosen the retaining screws 1/2 a turn and wiggle the rail on the reciever and check runout. I bet you get more than .005.

 

[Show Me]

I am not sure that a "proper set of scope rings" would provide closer tolerance. I think maybe a one-piece mount provides closer tolerance control because any actual error in either position or angle is spread over a much longer distance than the very short distances in each scope ring. AND the one piece mount is far more rigid which prevents torsional stresses that add to the potential for error. The best scope rings try to address this torsional stresses issue by machining both of the rings in one pair to be sold together in ONE operation TOGETHER, which at least reduces the potential for torsional stresses, but does not eliminate it (since the clamping rail on each scope has its OWN angular and posiitonal tolerance).

Jim G

Ok your right it those darn under age Chinese workers

 

[JimGnitecki]

I meant the screws that attach the rail to the receiver.

To prove my point, remove the optic, loosen the retaining screws 1/2 a turn and wiggle the rail on the reciever and check runout. I bet you get more than .005.

The OEM rail on the rifle was never touched - never unbolted.

 

[JimGnitecki]

Ok your right it those darn under age Chinese workers

I suspect that BOTH the TryGlo and the Wheeler rails were made in China, but one of tose 2 Chinese sources does better CNC machining.

Jim G