sheared base screws

[live2huntmt]

While at the range yesterday I noticed my scope was loose. When I came home, I removed the scope and found both forward base screws broken off. I was able to remove them from the action, and replaced them with new ones. I torqued base screws to 20 in-lbs and put the scope back on. Back at the range today, after 15 shots, I noticed the scope base was loose again. Came home and found the 2nd from front screw sheared off and the other 3 all loose. Other than going up to #8-40, what else can I do? Also, what could be wrong that is causing this?

Christensen Arms Ridgeline
300 RUM w/ Area 419 Hellfire brake
Nightforce A295 rail
Nightforce 6-screw ultralight rings
Nightforce NX8 4-32x50

 

[CVCOBRA1]

First Question......
Are you shooting this in a lead sled?

 

[bigngreen]

Good screws and bed the rail but clean both surfaces so it glues the rail as well. Heavy optic, light rifle high recoil and good brake with high exit pressure do this. I like to epoxy and pin rails for this kind of stuff.

 

[Montana73]

What? Epoxy MOA rail to the receiver? How would you ever get it off if needed?

 

[live2huntmt]

First Question......
Are you shooting this in a lead sled?

no...just a front rest and rear bag

 

[live2huntmt]

Good screws and bed the rail but clean both surfaces so it glues the rail as well. Heavy optic, light rifle high recoil and good brake with high exit pressure do this. I like to epoxy and pin rails for this kind of stuff.

I definitely do not want to epoxy my rail to the action!

 

[bigngreen]

I definitely do not want to epoxy my rail to the action!

Ya you need to or get it pinned. I epoxy every one I do, to remove you just have to heat it and the epoxy releases.

 

[bigngreen]

What? Epoxy MOA rail to the receiver? How would you ever get it off if needed?

It's easy to remove, some heat from a heat gun or heat a receiver wrench and slip it in the action so it warms the epoxy, same for popping a glued action out of a stock.

 

[CVCOBRA1]

Use iso-alcohol to clean screw holes and screws from any possibility of oil. Also clean the bottom of rail and top of action. A drop of BLUE loctite on each screw and bottom of rail. Torque to spec. Can always be removed with a little heat. If that doesn't work then your screw are either too long or your holes are not tapped deep enough. Had an X-bolt where the latter was the case.

 

[Montana73]

It's easy to remove, some heat from a heat gun or heat a receiver wrench and slip it in the action so it warms the epoxy, same for popping a glued action out of a stock.

ok, what brand of epoxy do you use? Might want to try as you indicate.

 

[bigngreen]

Locktite does nothing for shearing screws only makes it a pain to remove screws.
I use the same epoxy I bed the rifle with, I bed both the action and rail at the same time.

 

[CVCOBRA1]

I'll call you on that. If the screws were never tight to begin with they will shear at any stress. That is why I say screws too long or holes not deep enough.

 

[bigngreen]

I'll call you on that. If the screws were never tight to begin with they will shear at any stress. That is why I say screws too long or holes not deep enough.

Screw length is step one not locktite!

 

[Buck Fever]

If you rough the bottom of your scope rail and use mold release on your receiver, you can get your rail bedding to stick to your rail and not the receiver.

If you use a one piece rail, the recoil forces will be better distributed among the four screws.

Also, when you torque the rings on the base, you should push forward on both the front and rear rings so that both rings are actually resisting the recoil force.

Lastly, some screws are better than others.

If none of that solves the problem, start looking for a rail that has a recoil lug which takes the shear force off the screws.