Nightforce front base keeps coming loose

[Rflshootr]

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.

ABSOLUTELY CORRECT! Definitely check this! And if this is the case, it will hurt accuracy.

 

[Radman]

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

I clean my holes & threads with alcohol, put glue on each, then tighten the fool out of them, (sometimes to the point of stripping the head : ). This has always worked great for me, but I also baby a scope like it is glass as well.

 

[6.5-300 BEE]

I use red Locktite on everything. If you ever need to take apart, hit it with a needle MAPP torch.

Never a problem.

 

[7Rum Slayer]

Chamberman, I made a call to my gun smith last night and he mentioned that very issue. Something I would not of thought to check. I also took a peak at the old barrel that just came off that rifle and indeed very light marks on the tenon threads from the front screw. My smith also said bring it to him and he will drill out to 8/40 free of charge. Thanks again for sharing all the knowledge. Jason

 

[DSheetz]

I like to follow the manufactures recommended guide lines on product usage . As we go along in life we find out what will work for us by experience and by asking questions of others that have also had some experiences in that area of life . I also like a good quality one piece base set up that has been bedded to the action using a good release agent on the action so that I can remove it later if need be . For me I think that I would make sure that the screws aren't bottoming out or stretching and leaving a little play between the base and action . Over repeated use screws stretch and will weaken . The smaller a screw the more often I will replace them maybe just one or two uses . I have used loc-tite products and for me I find that they have a usage guide line for a reason . I may want to take a broken screw out some day with out needing to get it drilled or machined out . I have found over the years that the closer the fit with out gaps puts less stress on bolts and screws and keeps things in place better , more contact means more gripping power . I have also noticed that when torqueing bolts and screws there are some guide lines, some manufactures say to lube the head of bolts and screws while others want them dry without lube . lube on the head will give you more torque as it lessens the friction and allows the head and base metal to slide together without pulling metal from each other that is counted as torque . Friction = amount of torque applied = amount of holding power applied to two separate parts .

 

[PddPdd]

IMO, The proceeding ideas are all good practices but based on my recent experience you may not be addressing the root cause of the problem.

Question: Is your front base made of aluminum?

If yes, The mounting screws may be seeing significant tension load changes due to the thermal expansion/contraction of aluminum. This could act to loosen the screws over time or break the bonds of the loctite and other adhesives. I believe the larger screws and mounting adhesives may overcome this issue, in practice, without addressing the root cause.

Onother method to address this would be to use a base material with lower thermal expansion than aluminum such as steel or titanium.

Best of luck in finding what works best for you.

 

[7Rum Slayer]

Thanks again, all replies are greatly appreciated. bases are steel and night force did supply me with plenty of extra screws so those are new as well. I'm gonna go with 8/40's as my smith offered to do so and then bed for a perfect fit. Jason

 

[DSheetz]

7Rum Slayer , That sounds like a good plan . I believe I would also if it were me in your place .

 

[Edd]

My education is mechanical engineering & manufacturing coupled with almost 40 years in the field of designing and making things.

What has the greatest resistance to shearing, a .125" diameter rod or a tube with a .265" OD and a .165" ID?

 

[PddPdd]

What has the greatest resistance to shearing, a .125" diameter rod or a tube with a .265" OD and a .165" ID?

.265" diameter tube is stronger in shear based on cross sectional area assuming materials are the same. .033 vs .012 square inches.
I accidentally used circumference forumula instead of area earlier.
ntsqd is correct!

 

[ntsqd]

What has the greatest resistance to shearing, a .125" diameter rod or a tube with a .265" OD and a .165" ID?

groan, gonna make me do that math stuff? Not sure where you're going with this, but......
Shear strength is purely cross-sectional area times ~57% of YTS if a metal. Its more complicated than that, but that's a decent RoT for guesstimations and since my stuff never flies and rarely has to float a guesstimation has been good enough 90+% of the time.
More area in shear = greater resistance to shear.
Tube has a cross-sectional area of OD(area) - ID(area) or .05515 in^2 - .02138 in^2 = .03377 in^2
Rod has a cross-sectional area of OD(area) or .01227 in^2
Tube has the greater area in shear, so assuming the same YTS as the rod it wins. Now if the tube is 12L14 and the rod is 17-4 H900, that's different......

 

[DSheetz]

Maybe the rod is ER70S

 

[ntsqd]

Then it's slightly better than the 12L14, but not in the same ballpark as the 17-4 H900.

 

[Edd]

.265" diameter tube is stronger in shear based on cross sectional area assuming materials are the same. .033 vs .012 square inches.
I accidentally used circumference forumula instead of area earlier.
ntsqd is correct!

What is the circumference formula you used?