sheared base screws

[J E Custom]

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 4-32x50View attachment 189069View attachment 189070

This is not uncommon with light weight , hard recoiling rifles with heavy scopes.

Two fixes that I use are to increase the size of the screws or use a Scope base with a recoil lug or set screw to take the recoil, Near Manufacturing calls it his Pro lug. Others have a set screw that go's in at an angle and contacts the front of the ejection port to relieve the screws of the recoil.

Leupold makes some good steel bases with different screw sizes for different actions and all that Is needed is to tap out the small screw holes the 8's or 10's.

J E CUSTOM

 

[Wedgy]

If your rail has a wider radius than the action it will only make contact in the center instead making full contact(red line is the rail, blue is the action), and it will be very weak side to side. In Tony Boyer's book he addresses this by milling the center of the rail lengthwise to ensure that the edges contact the receiver. I don't have a mill so I bed all mine, and tap to #8-40. Ken Farrel sells taper head torx screws I like.

 

[thwatson2]

tap larger 8-40 and torque to spec. Make sure you can finger screw the screws and no binding as you may have holes in receiver not aligned to mount. You don't want binding. use good quality screws and loctite or not, your choice. I have never had this happen, from 300RUM to 338 RUM to 375 h&h to 50 bmg. You have something wrong here. first thought is a crappy batch of screws.

 

[parshal]

All suggestions here are certainly fixes. Before I pinned or tapped for 8-40 I'd check your screw length to be 100% certain they are not too long. If they are a fraction too long and the rail is minutely loose the screws can easily break. You can bed the rail to ensure it's got 100% contact as well if you don't want to glue it to the action. Try those two things first then go shoot. Check the torque after a few rounds and see if it's loosening. If it is, the next step is to glue it to the action (heat will easily remove it), pin it or move to 8-40 screws or some combination of that. I have drilled/tapped for 8-40 myself on the mill but I'd still try the other stuff first before I started drilling. 6-48 screws have been used for a very long time so they do work if they fit correctly.

 

[Tim Sharp]

I might double check with Nightforce (assuming the screws used came with the rail) and ask them if they had a bad batch of fasteners. In your photo the screws appear to be SS. I would try some quality high strength black oxide screws (heat treated) to see if it mitigates the problem. https://www.brownells.com/gunsmith-...-thread-150-length-sku078018615-335-1574.aspx

 

[Glenn Tullius]

I absolutely refused to believe my screw length could possibly be to long for a year... what a rookie bonehead I was! Check the screw length, if for no other reason than to eliminate that possibility!

 

[codyadams]

The front screw is the only one that could be too long and would not be immediately obvious, as it would torque down on the barrel tennon. If any of the other ones were too long, they would be locking up the bolt or not allowing it to go in the action, as the only thing for them to torque down on would be the bolt/bolt lug itself. Always make sure the front one isn't too long though, as is being stated.

The best solutions have been stated already. #8 screws, pin, and epoxy. I have epoxied in the past and then removed rails, it is not hard. On my 9 lb .338 Norma Mag, I opened screws up to #8 and bedded/epoxied my 1 piece DNZ mount in place, with lock tight on the screws. Lapped the scope rings and installed the optic. I have around 150 rounds fired with zero issues.

 

[live2huntmt]

The front screw is the only one that could be too long and would not be immediately obvious, as it would torque down on the barrel tennon. If any of the other ones were too long, they would be locking up the bolt or not allowing it to go in the action, as the only thing for them to torque down on would be the bolt/bolt lug itself. Always make sure the front one isn't too long though, as is being stated.

The best solutions have been stated already. #8 screws, pin, and epoxy. I have epoxied in the past and then removed rails, it is not hard. On my 9 lb .338 Norma Mag, I opened screws up to #8 and bedded/epoxied my 1 piece DNZ mount in place, with lock tight on the screws. Lapped the scope rings and installed the optic. I have around 150 rounds fired with zero issues.

I absolutely refused to believe my screw length could possibly be to long for a year... what a rookie bonehead I was! Check the screw length, if for no other reason than to eliminate that possibility!

I checked my front screw length by installing only the front one and it tightened the rail to the action...I was worried because it only engaged for 2.5 turns. I then removed the rail and checked to make sure the other three screws were able to go all the way thru the action, and they could. It's at my gunsmith now getting 8-40s put in. I will also epoxy it.

 

[BHP9]

I clean the receiver and the bottom of the scope base, the a drop or 2 of red loctite on the receiver, place the base on and blue loctite the screws.

Never had a problem. #6 screws.

 

[DSheetz]

Screws and bolts come in different grades make sure you get a grade 8 black screw even for a S.S. receiver as you won't see them any way . It used to be that torque specs told you to wet or dry torque for screws and bolts , wet torque refers to lubed especially the shoulder of the screw so that friction doesn't cause a false reading . You may try laying a lap in the bottom rings to see if the mount is true and you don't have undue stress on the scope and base's . When you bed base's to your action you don't really glue them to your action as you use a release agent on your action and are just filling any gaps between the base's and action so as to get 100% contact between the two . You will just line up the screws and snug them until the bedding cures , then remove the base's and clean the holes out , then torque the screws . As has been stated before make sure that the screw holes are clean and that the screws aren't bottoming out . I have also seen a foot pound torque wrench used by mistake instead of an inch pound torque wrench but then the screws usually break during the process when that happens .

 

[codyadams]

I checked my front screw length by installing only the front one and it tightened the rail to the action...I was worried because it only engaged for 2.5 turns. I then removed the rail and checked to make sure the other three screws were able to go all the way thru the action, and they could. It's at my gunsmith now getting 8-40s put in. I will also epoxy it.

You should be squared away then

 

[mo]

This solves a lot of problems and it works fantastic. I've installed them on 3 of my rifles. I'll post a link.
http://accuracyassured.com

 

[mo]

I don't suggest this, but I installed one on a 7wsm without istall

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 4-32x50View attachment 189069View attachment 189070

This will take care of the problem you're having.

 

[Buck Fever]

Is that like the American Rifle Company Nucleus recoil lug? It has a tab on the top of the recoil lug that the scope rail bears against.

I had a spare and used it on a Savage project. I bedded the rail to the receiver and the rail to the lug. I did have to notch the rail to fit. I expect it will work well.