View Full Version : scope mount

June 14, 2010, 10:31 AM
Gentlemen, I have a issue with a scope that loses center after rifle warms up. Its a nice scope (Nikkon Prostaff 3x9x40) Mounted on a Ar15 with a 20 in barrel. When I bought the scope I had the mounts installed onto the scope. I took that home and mounted onto my rifle, I didn't use lock-tite or any product like that. At the range the rifle starts to lose center, and when I check the mount screws are only snug, and I am sure they were tighter than that from the previous range visit. Should I be using something like Loctite Threadlocker Green or Blue. Any help ? Thanks for taking the time to read my thread.

I know I should have included pics, but the camera is at the girlfriends house and I cant get to it till next weekend.

June 14, 2010, 11:04 AM
How many shot are fired before it starts drifting?

June 14, 2010, 11:21 AM
About 20 or 30, this happened in two consecutive range visits.

June 14, 2010, 11:27 AM
Definitely use something like LocTite blue. Green would work OK but it won't hold as well. FWIW, I have never had a sight mount on my AR come loose, but there's always a first time.

June 14, 2010, 12:46 PM
Thanks , I will give that a try

June 14, 2010, 08:56 PM
could it be the barrel is just getting hot?

June 15, 2010, 10:43 AM
OLddav, Thanks for your suggestion. The barrel does warm, but I shoot in 5 shot groups and then let it cool while I look at the group through my spotter scope and decide what I did right or wrong. No it doesnt get hot but it does get warm.

June 15, 2010, 06:30 PM
I shoot 3 shot groups when I go to the range. At that point I open the bolt stand the rifle up and wait approx 10 - 15 minutes. I'm sure the barrel is not stone cold but it does cool quite abit and provide consistent groups. I'm no expert but this does work for me. Good luck and post the results of your next trip to the range, I'll be looking for it in the future.

June 15, 2010, 08:57 PM
Does your rifle have the military style plastic handguards or a free float rail/tube?

With the military style handguards, you are essentially resting the weight of the rifle on its barrel. As the barrel heats up, it will naturally throw shots since the weight is changing between shots. A free float rail/tube cures that problem.

June 16, 2010, 12:15 AM
DnPRK, Thanks for the reply. It does have the free float rails. I will gets some loctite blue before my next range visit and post results. I am hoping that its is loosening up, I would hate to think my reticle is loose. Its not a cheap scope.

June 16, 2010, 10:03 PM
What type of mount?

June 17, 2010, 12:15 AM
Gun money, the answer will have to wait till next monday and I will post a picture.

August 5, 2010, 10:34 AM
Finally got around to getting Loctite thread locker blue from lowes for 5 buck small tube. Mount is a Weaver high rise, scope is Nikon prostaff and rifle is a RRA ar15 with metal free float quad rail. I got the scope close to center with laser, then loosened the 4 screws one at a time and applied the loctite blue then tightened and did the same with next screw. I let set for half hour then ran 100 rounds down range in 5 shot sets while zeroing the scope. As I went the scope nevered wander off as it did before. Last 20 rounds I let the barrel heat up and it still stayed. So this worked for me, there may be other solutions to this problem but this one worked. Thanks to Scorch for his suggesting the loctite blue and thanks to everone else for their input.