Nightforce front base keeps coming loose

[7Rum Slayer]

Hello to all and hope all is well. this is my first post so please forgive me as I learn to navigate my way through. I have 2 model 700 rifles both have nightforce 2 piece 20 moa bases wearing nxs scopes with NF rings. 7mm RUM with bartlein barrel very accurate shooting 155 Hammer Hunters and a 300 RUM shooting 181 Hammers as well. I recently received my 7 Rum back from gunsmith with new barrel and he was supposed to tap out 6/48 screws to 8/40 as I had the front base come loose years ago on a mule deer hunt. The gunsmith forgot my request. So shooting long range last week to verify b.c. and drops my 1/2 moa rifle shot so poorly I knew something had to be wrong. Yep, took the scope off and again front base is loose. After a call to the fellow who put the new tube on he advised to try blue loctite so I did. I have not made it back out to shoot but I'm second guessing this after the fact. I was considering JB weld or pro bed 2000 to bed the base, even considered permanently bedding them. Has this happened to anyone else using similar setup and what was your fix? I do not want to pop the barrel off to tap out 6/48's. Also happened to my 300 Rum a few months back that rifle's bases has fingernail polish holding the base screws and still worked loose. Another question, has anyone taken their scope off of the rail put back on and verified zero long range? Seems I tested that years ago but only at 100 yards. Both rifles have side discharge muzzle brakes and I have never shot with a leadsled. I always push the rings far forwad in the rail as well. My hunting scenarios are almost always backpacking miles from my truck so I can not afford another murphy moment while hunting. I will ad this forum has been a wealth of knowledge for me even after 20 plus years of dedicated long range shooting. Thanks for any info in advance and always remember; none of us know more than all of us! Jason

 

[LaHunter]

Prepping the screws, screw holes, and contact surfaces before installation is important. I have used acetone or alcohol to clean / degrease everything. The screw holes can be a little stubborn at coming clean. Q-Tips can be useful. The contact surfaces need to be 100% clean and dry, no oil.
I personally prefer a 1 piece pic rail vs a two piece base system, especially on magnums, but that is just my personal preference. I have this with a 5-20X56 NF SHV (29 oz) w/ NF rings on my unbraked 7mm rem mag, so not quite the level of magnum as the RUMs, but a significant recoil.
The blue Loctite can help keep the screws in place and not working loose.
Do you have a torque wrench? What are you torqueing the base screws to?
Maybe call NF CS and see what they say, they have been helpful every time I have called them

Good Luck

 

[rsmithsr]

I think the above PLUS epoxy under the base is a good idea.
clean every this is very important. I too like once pc bases on open top receivers

 

[ntsqd]

Acetone can leave a thin film behind. Iso-Propyl Alcohol doesn't, but it also isn't quite as effective of a solvent. If you're going to use those to clean/degrease with, use the acetone first followed by the IPA. Mostly I use either GunScrubber or Brake Cleaner (carefully!) to degrease screw holes. I was taught way, way back to use blue Lock-tite on base screws and have yet to find a reason to discontinue doing this, but others with vastly more experience (I've likely only mounted 200 to maybe 300 scopes in the last ~30 years) may feel differently.

Bedding the bases (I'd do both since you're there) should remove any fit problems that might result in a base loosening in use.

 

[7Rum Slayer]

Thanks for the replies. I did prep and clean the holes with acetone and a q tip then blew the holes clean with degreaser. The first time this happened a call to nightforce was my first course of action and they were kind enough to send me a few brand new screws and recommended I cleaned all holes thoroughly. I use a wheeler torque wrench and torqued to 25inch lbs. as per nightforce recommendations. I realize these are both heavy hitters as far as recoil but I treat them both like high performance race cars and not daily drivers, meaning I try not to shoot them any more than is necessary. I have several other rifles to shoot and hunt with but the 7 RUM is and has been my main mamma jamma for several years now. If I bed the bases with JB weld and use a good release agent being careful not to get the epoxy into the screw holes but do not remove the base, will the base still pop free in the future if needed? I read that with heat applied they will remove but I have no experience with this. I'm thinking of trying it. Thanks again, Jason

 

[Bob Wright]

I had a Smith open 3 of the 4 to #8 and bedded my 1 piece pic rail. Never had it come loose and since I have tamed it down with a brake.
I have a Rem 700, 7RM. My scope is lighter than the NXS BY 30% I'm guessing. But, 3 of 4 is working.

 

[Gone Ballistic]

You mentioned that you didn't want to drill and retread to 8/40's but I highly recommend you do. The enertia is almost double on your split base setup. I retapped so many rifles, even using one piece bases, because when you are using a scope like a Nightforce or any other weighing above the 24 ounce mark, especially shooting any rifle creating over 15 ft pounds of energy, 8/40's are the only size screws to use, loctited with 25 inch pounds of torque on each screw. I have seen smaller screws shear as well as ruin binding holes in base mounts. Does not take much cost to fix a huge potential problem.
Just read you are using JB Weld. Acetone will work well to remove it. If using it doesn't get down to the bottom of the threads, don't apply heat until the Acetone has dissipated or you will far worse problems than removing the screws!

 

[Bob Wright]

Thanks for the replies. I did prep and clean the holes with acetone and a q tip then blew the holes clean with degreaser. The first time this happened a call to nightforce was my first course of action and they were kind enough to send me a few brand new screws and recommended I cleaned all holes thoroughly. I use a wheeler torque wrench and torqued to 25inch lbs. as per nightforce recommendations. I realize these are both heavy hitters as far as recoil but I treat them both like high performance race cars and not daily drivers, meaning I try not to shoot them any more than is necessary. I have several other rifles to shoot and hunt with but the 7 RUM is and has been my main mamma jamma for several years now. If I bed the bases with JB weld and use a good release agent being careful not to get the epoxy into the screw holes but do not remove the base, will the base still pop free in the future if needed? I read that with heat applied they will remove but I have no experience with this. I'm thinking of trying it. Thanks again, Jason

It will come right off easily if you use a release agent on the action.

 

[ntsqd]

I think it is a mistake to view the mounting screws as being in shear. Any pins used are, but these screws aren't and if they are they won't live. They're there to clamp the bases to the action and it is the friction between those two surfaces that resists the recoil. Flywheel bolts aren't in shear, they aren't big enough nor are they numerous enough to transmit the crank's power. It is the clamp-load's friction between the flywheel and the crank flange that transmits the load. This is why the fit between the two surfaces is so important. It is also why the bolt's install torque is so critical.

The same is true for these screws and for the fit to be exact. Going to bigger screws isn't to increase their shear strength (though it will do that too), it is to increase the install torque which increases the clamp loading. Bedding the bases to the action improves the fit, which improves the friction between them.

I used Johnson's paste wax for release agent when I bedded the mounts on a project rifle.

 

[7Rum Slayer]

Thanks again for all replies. I feel the 8/40 screws plus bedding to the action will give me more confidence in the future. pain in the butt as I just got this rifle back from the smith but worth the trouble in my mind.

 

[rsmithsr]

pure smoke and mirror comment.
one to avoid

I think it is a mistake to view the mounting screws as being in shear. Any pins used are, but these screws aren't and if they are they won't live. They're there to clamp the bases to the action and it is the friction between those two surfaces that resists the recoil. Flywheel bolts aren't in shear, they aren't big enough nor are they numerous enough to transmit the crank's power. It is the clamp-load's friction between the flywheel and the crank flange that transmits the load. This is why the fit between the two surfaces is so important. It is also why the bolt's install torque is so critical.

The same is true for these screws and for the fit to be exact. Going to bigger screws isn't to increase their shear strength (though it will do that too), it is to increase the install torque which increases the clamp loading. Bedding the bases to the action improves the fit, which improves the friction between them.

I used Johnson's paste wax for release agent when I bedded the mounts on a project rifle.

 

[ntsqd]

pure smoke and mirror comment.
one to avoid

My education is mechanical engineering & manufacturing coupled with almost 40 years in the field of designing and making things. What do you base your accusation on?

 

[Chamberman]

Last question... Which I have not seen from anyone.
Is the front screw above the barrel thread tenon touching/ bottoming out on the barrel thread tenon????
If so, that is the problem.
Remove that screw and look at the bottom of your front screw and also look at the barrel threads.
If the bottom of the screw is galled and the barrel threads are galled, the front screw needs trimmed back...
Very, very common issue.

 

[Rflshootr]

Bed the bases to the action with release agent. That gives a perfect match to the action and increases surface area to the maximum that it can be. I use Loctite 222 (purple) on small screws which it was designed for. Still easily removable if need be. Doing those 2 things, you shouldn't have a problem.