XLR stock issues

codyadams

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There is at least one component that is adding to the "loosening" of take down screws in my theory.
Slickness of smooth anodized aluminum chassis against the slickness of fine surface finishes of the receiver. The friction on receiver and chassis when clamped down with torqued takedown screws is diminished greatly.
If the recoil lug is not fitting tightly in the mortise, and the receiver is moving, that would tend to "yield" those 2 takedown screws at some point during firing. After all, they need re-torquing, so those screws aren't rotating loose, they are getting "yielded". If one has to continually re-torque after shooting sessions, those screws cannot do the job by themselves.

Has anyone bedded the recoil lug/ mortise?
These chassis are cerakoted, either magnesium or aluminum
 

Bob Wright

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These chassis are cerakoted, either magnesium or aluminum
If it were mine, I would torque it again, mark the head of the bolt to the chassis (torque stripe in aviation speak) to confirm it's not backing off and if the screw can rotate (yet again after firing) under the same torque, the screw is stretching permanently.
That would indicate the screw is taking the recoil load in shear and tension. Should only be tension if the action isn't slipping.
Then, I would epoxy bed it and using brand new screws. Too bad they don't sell a higher tensile screw (?)
 

Rick Richard

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If it were mine, I would torque it again, mark the head of the bolt to the chassis (torque stripe in aviation speak) to confirm it's not backing off and if the screw can rotate (yet again after firing) under the same torque, the screw is stretching permanently.
That would indicate the screw is taking the recoil load in shear and tension. Should only be tension if the action isn't slipping.
Then, I would epoxy bed it and using brand new screws. Too bad they don't sell a higher tensile screw (?)
I can’t see an action screw/bolt yielding at 65 INCH pounds or am I wrong?
 

BrentM

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Seems like everyone in my circle beds everything. All have issues at some point they say. Me too but I’m stubborn and only bed if things are really off. For example my actions stay tight, no bedding. Usually what happens is the zero will shift and I’ll adjust once and it’s good to go after. My xlr 4.0 has shifted 1x and I’ve left it alone. I should bed it tho. Ha ha
 

ntsqd

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I can’t see an action screw/bolt yielding at 65 INCH pounds or am I wrong?
It would be the recoil impulse that is yielding the screws, not the install torque.

For an ultra-light build with a Howa action I was able to source M6x1.00 Titanium button heads from somewhere on the net, but I doubt that metal is the solution here. Maybe if you can find some made of 17-4 H900 or a similar high tensile strength alloy?
 

Rosebud

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You can use the farmers technique for tightened stuff, get it as tight as possible then add another quarter turn. If it doesn't make a popping sound when its broken free it wasn't tight enough. Not recommended this for his rifle. Things always loosen on farm equipment. 😁
 

Bob Wright

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I can’t see an action screw/bolt yielding at 65 INCH pounds or am I wrong?
That's the initial torque. When firing, if the action is allowed to move, it puts another load on the screws. If those screws are loosening as others have said, they're not rotating, they are yielding. That's my premise.
As for the brake, scope, levels coming loose, I would also say that may be a secondary effect to the action slamming. The only way to test it is to get the action secured and test it again.
My wood stocks and composite ones are pillar bedded and the problem does not exist. Test....
 

ajvinyard

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Harmonics affect more than just your group size, that is the reason most of us put blue Loctite on the scope base screws or they run the risk of coming loose. This is very common in the mechanical and industrial world and so they use lock washers, lock nuts, or Loctite, or even oversized fasteners that can be torqued tight enough to overcome the harmonics. They even see a non critical steel part crack just from vibration. Harmonics effects on fasteners can be a very difficult thing to overcome, you can try a non permanent form of Loctite and it should help. Sometimes you may want to change the screw if it has a screwdriver slot to an socket head or bottom head alan screw for removal later.
 

Bob Wright

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Seems like everyone in my circle beds everything. All have issues at some point they say. Me too but I’m stubborn and only bed if things are really off. For example my actions stay tight, no bedding. Usually what happens is the zero will shift and I’ll adjust once and it’s good to go after. My xlr 4.0 has shifted 1x and I’ve left it alone. I should bed it tho. Ha ha
I would say no. If you have no more issues, it's fine. Why are others going thru it 2x or more, something is wrong.
 

Bob Wright

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You can use the farmers technique for tightened stuff, get it as tight as possible then add another quarter turn. If it doesn't make a popping sound when its broken free it wasn't tight enough. Not recommended this for his rifle. Things always loosen on farm equipment. 😁
The Russian Aerospace requirement is simply after contact turn it a fraction of a turn depending on the fastener size and pitch. No torque required. Just let the thing stretch and rebound in service.
Not the US.
 

ntsqd

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Sort of, there are "Torque to Yield" applications in the US and Europe. One time use fasteners carefully torqued until they do yield.
There are also "Torque-Angle" applications where the fastener is torqued to some low point, and then rotated so many degrees past that point.

Most lock washers aren't worth the trouble that they cause. Star type are particularly good at making an electrical connection, but none of them are terribly effective at locking a fastener in place and split washers are particularly good about breaking in service and leaving the fastener loose.

What does XLR do differently from all of the other chassis mfg's, or is this a problem that they all suffer from?
 

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