Scope mounting problems

My Gamo Hunter 440 Refurb is still shaking scope rings loose and I've run out of ideas on how to correct it.  I'm starting to think ramp/riser width variance may be the cause but this part does not appear to be replaceable,

As described in previous post, problem began with 4X32 in Gamo-supplied rings, unable to keep rings from moving back on scope ramp/riser.  Based on online info and forum advice, had recently installed one-piece Accushot medium mount and Bushnell Sportsman 4-12X40 at same time.  Degreased contact surfaces screws and tapped holes with denatured alcohol, used blue LocTite 242 on threads and contact surfaces then let cure 24 hours. (Did not install scope-stop screw because it did not permit ideal scope positioning.)   Noticed a zero shift within 150 shots, found Accushot had moved back about 1/8" yet base screws were tight, rezeroed and continued shooting, by 250 shots it had moved another 1/4" back.

Once again I removed scope and mount, degreased and reassembled with blue LocTite (with scope-stop screw at optimum depth).  Within 200 shots experienced another zero shift, found scope mount had moved back about 1/16".  The only assembly glitch I know of is: after LocTite cured (of course) realized I'd forgotten to degrease/loctite scope-stop screw after careful depth adjustment.  Now am debating whether to try again, or, sell this 440 for "iron sights only" use and replace with new 440 or CFX from Natchez.
 
Once again any additional advice as to what I may have overlooked, or screwed up, will be sincerely appreciated.

Curtis

[Gene_SC]

The only thing that ever worked on my Gamo Hunters, S1K's is a one piece accushot mount with stop pin hole. Rings are worthless on those air rifles. They will never hold unless you buy the accushot 2 piece mounts and use the stop pin hole to lock back ring in place. I mention accushot mounts because they are the cheapest you can buy. I have about 8 Gamo's now and the only have accushot 1 piece mounts and scope or mounts have never moved since I put them on.. Be sure and buy a air gun rated scope as well. BSA makes several inexpensive air gun rated scopes you can choose from.

Good Luck

Gene

[Gene_SC]

The only other mount I can think of that would be as good and maybe a bit better is the BKL mounts. There is a link in the GTA Mall for them and you can buy them from Straightshooters as well. The Peak swears by them and of course they are kinda on the expensive side.. The Peak told me she was not high maintenance but I beg to differ.... LOL She just has excellent tastes I guess.. hehe

Gene

[longislandhunter]

Hi Curtis,

I have quite a few GAMO rifles with the same power plant that's in your 440 and I have Accushot 1 piece or 2 piece mounts on all but one of em and they've held rock solid since the day I installed them. I can't think why your mount isn't holding... it should hold if all the surfaces are clean prior to installation. Only thing I can think of with the stop pin is that perhaps it wasn't seated deep enough. The key with the stop pin is to align it directly over the hole and after tightening the mount down securely onto the scope rail then crank the stop pin down into the hole until you feel stiff resistance. Once you do that you know it's seated as deeply as it's gonna go. If thats done and the mount base is really tightened securely then the mount shouldn't move.

However,,, if even that doesn't work Gene is correct,,,,,, the BKL 260 six screw mount will hold without any doubt. I have one of those mounts and they are incredible!! If you have a rifle that just will not permit any mount you try to hold then put on the BKL,,, it will hold !!! It's a little pricey but it will definitely hold where no other mounts will.

JEff

Upon disassembly found one-piece Accushot scope-stop screw was sheared right where diameter reduces from 5 mm to 2.8 mm, as stated previously probable cause was I'd tightened only to light resistance and had neglected to LocTite same when assembling.  Fortunately Accushot mount came with spare hardware including another stop screw.
Degreased everything again, even used alcohol-dipped QTips in drill motor to insure all tapped holes were free of any lubricant.  Added hardened-steel 5 mm flat washer on each 5 mm base screw and blue LocTite on threads, washers were to reduce friction, they allowed additional 1/4 turn or so when tightening to clamp tighter onto dovetail.  Then installed scope-stop screw with red LocTite and tightened down securely to lock mount in place. Reinstalled scope, positioned and secured using blue LocTite on ring threads.  Then degreased once again where  mount base clamps dovetail, on each side, and added very thin bead of red LocTite, applied with a toothpick.  
After that I let cure 10 minutes, fired two pellets to settle scope and mount, rechecked all screws then let assembly cure for 72 hrs ... 24 hrs was supposed to be adequate but was taking no chances.
Have fired 100-150 pellets since and no apparent scope movement or zero shift ... am keeping my fingers crossed this finally did the trick.
I sincerely appreciate all advice provided, without access to your collective experience I would probably have given up on this refurb rifle.
Curtis

[longislandhunter]

Glad it worked out for ya

Jeff

[PBJ]

I have two 440's that were doing the same thing. I use a scope stop and that seems to do the job. I am using two piece Accushot rings with the stop pin into the hole. I think the aluminum in the mounts is stretching from the pressure of the steel screws and what we see as getting looser is really just metal creep. Also, I use Leepers Bug Busters and they are fairly light. My next step will be to have an absolute stop block added by my gunsmith to ensure that nothing can move back. However, the laws of physics tell us that something will have to absorb the loads and the forces involved will eat a scope over time.