Scope sliding in rings

RigPig

New Hide Member
Jan 30, 2018
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#1
Newer member here and new to bolt guns. I’ve had numerous gas guns with scopes and no issues with quality mounts. Knowing this, when I was assembling parts for my long range rig (Bergara HMR 6.5CM, Vortex PST GenII 5-25x, Seekins 20moa rail and Seekins medium rings), I made sure to go with what I thought was a quality mounting setup. During initial break-in (50rds per manual), I noticed POI shifting. Upon further inspection, I noticed my scope had slid back about .125” in the mount. I used a Fat Wrench to torque the caps to 20 in/lbs, rings to 55 in/lbs, and rail to 20 in/lbs initially, all with clean/dry threads and blue loctite. Upon return from the range, I re-set the scope in the rings and torqued them to 25 in/lbs and rezeroed. I ran the rifle in a 100rd +/- match a couple weeks ago, and noticed when I got home that the scope had, again, slid back. I was under the impression that with quality rings/rail, I shouldn’t have to lap them, and I don’t have a kit to do it. Should I have the rings lapped or is there something else going on? Like I posted before, I haven’t had this issue with several ADM mounts on ARs over the years.
 
Jan 2, 2003
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#2
I have 3 sets of Seekins rings and haven't had an issue with scope slippage. I'd call Seekins and talk to them. I've never had to lap Seekins rings and I wouldn't lap a quality set of rings. I would try mounting the scope after degreasing everything and use a bit of rosin to give the rings more grip.
 

RigPig

New Hide Member
Jan 30, 2018
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#4
You do have a quality setup. Lapping wouldn't help that. There's just no way it's just shifting like that. That's a 30mm main scope tube. What size Seekins rings do you have? My guess is you have 34mm rings.
That would be the obvious problem. Torque it as much as you want. I'll bet it's 4mm too large.
I can’t tell if you’re serious or not. 34mm rings wouldn’t clamp onto a 30mm scope at all. 34mm is over an 1/8” larger than 30mm. The scope would be rattling in the rings.
 
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RigPig

New Hide Member
Jan 30, 2018
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#5
I have 3 sets of Seekins rings and haven't had an issue with scope slippage. I'd call Seekins and talk to them. I've never had to lap Seekins rings and I wouldn't lap a quality set of rings. I would try mounting the scope after degreasing everything and use a bit of rosin to give the rings more grip.
This was kind of my thought. I didn’t know whether to lap them and go on with life or look for a remedy from the manufacturer. I do tend to seek out Seekins accessories, so I’m familiar with the company. I’m sitting here bored at work and my rig is sitting in the closet at home. I’ll pull the scope this evening and look for anything obvious. The rash on the scope looks deeper from the bottom trunnions of the rings.
 

fdkay

Gunny Sergeant
Nov 27, 2009
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#6
I have had this happen more than once.
It is frustrating for sure.
I have a Burris XTR II mounted in the steel burris extreme tactical rings.
The rings appear well made and a quite robust, but I'll be damned if they didn't continually let the scope slip.
I, personally believe that it may be an issue of tolerance stacking.
I recently disassembled and carefully degreased, then applied clear adhesive tape to the scope rings, that seems to have done the trick.
 
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Fig

Janitor of the Hide
Mar 15, 2018
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#7
One would think, but there is a small aberration. 34mm rings aren't exactly 34mm when torqued down, nor are they perfectly round. This is why you torque down the screws in opposing sequence. You may very well be able to torque them down enough to hold the scope but not under recoil. All I can think of is they're the wrong size. Put a caliper on them. The rings and scope body have to be about the same size if they're sliding.

I have never used tape, but I have used release wax and bedded a scope onto rings.
 
Mar 24, 2018
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#9
Get a Wiha torque wrench. Maybe your torque wrench is out of spec. Or keep bumping up the torque, within reason, until it doesn't slip.
Or mount it up in a way that butts up against the turret housing.

I'm going to get absolute shit for this, but double-sided tape inside the scope rings if all else fails and you don't want to send them back.
*queue the horde of folks who say one or two thou is too much out of spec* *flamesuit ON*
 

Fig

Janitor of the Hide
Mar 15, 2018
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#10
You mean the green, poster-board mounting stuff? It's sort of spongy and foam like? I was thinking some of the super heavy electrical tape might work. That would probably work.

Why flame you if it works? Because it's hillbilly engineering? Sometimes it isn't worth trying to "fix" something. Sometimes it's plenty good enough to alleviate the symptoms. I will never discount the field expedient solution.
 

RigPig

New Hide Member
Jan 30, 2018
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#11
I remover the scope yesterday evening and inspected the rings for obvious burrs or high spots. I didn’t notice anything unusual. There was some oil residue in the ring saddles, and some thing waxy in the rear ring saddle, so I’ll clean them up and maybe swap caps around and retorque. I don’t like the idea of tape, but I may try that as well. What would be a maximum torque spec to keep in mind? Factory spec was 20, and as I posted, I tried that and 25 in/lbs.
 

RigPig

New Hide Member
Jan 30, 2018
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#14
Just buy some ARC rings, nothing will slip and a scope tube will look like new when/if you sell it. Worth every penny.
Unfortunately, too late on my scope looking new. She’s got some rash now. Not bad, but it’s definitely not buffing out. I do like the design of the ARC rings though. Pretty much failproof.
 
Likes: Wyzrd
Mar 16, 2008
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#15
Unfortunately, too late on my scope looking new. She’s got some rash now. Not bad, but it’s definitely not buffing out. I do like the design of the ARC rings though. Pretty much failproof.
Yeah, it sucks when stuff like that happens!

I had a NF 5.5-22 that slipped in a pair of NF steel rings, that was on a 375CT though, after torquing more the scope still slipped. ARC had just come out so I bought a pair of those, doing so solved the problem completely. I ended up selling that NF at a huge loss and put the rings on a PCP air rifle, lol.

3 pairs later and a bunch of scope swapping has proven ARC rings are the best rings I've come across. I'm about to buy my fourth pair.
 
Jul 24, 2011
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#18
Hmm.

The scope should not be sliding, obviously. The equipment your using looks fine and that is not even a particularly hard recoiling caliber.
I do loath the lock-tight though. Lock tight tends to make things inconsistent.

For what it is worth I make sure the scope and inside of the rings are dry and clean and that the cap screws are greased. Greased cap screws do actually provide more force than dry but I do it for the consistency of the load they apply. I have never had a problem @ 20 inch lbs with this procedure.

I agree with your thoughts that lapping is not something that is nessecarry with quality stuff nowdays. My thought is that the locktight is causing you to get a poor read on how much load you are actually applying and probably also making that load uneven. My only other thought is that your ring tops might be canted to one side or the other and not showing the same gap between top and bottom on both sides.
 
Oct 31, 2017
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#19
Primarily the issue with scopes slipping in the rings tends to be alignment, if the ring is not "square" with the tube of the scope, then just the edges of the ring are bearing against the tube. Make sure that the rings bear fully against the tube of the scope. Usually I'll mount the bottoms of the rings and lay the scope into them and see if it will freely rotate along the axis of the scope in the ring bottoms. If it "grabs" in the rings, that is usually an indication that one of the rings is canted or misaligned with the tube and needs adjustment. Avoid placing anything inside the ring that will reduce its diameter unless it is supplied with the ring. If you put shims inside a ring that is not intended for use with them, the reduced diameter may dent the tube of the scope when tightened. I've mounted probably over a thousand scopes and can't remember any problems if the rings were square and torqued properly. That includes 416's, 50bmg's and others I don't remember. If you're around Fairbanks, I'd be happy to give you some pointers in person.
 

RigPig

New Hide Member
Jan 30, 2018
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#20
Primarily the issue with scopes slipping in the rings tends to be alignment, if the ring is not "square" with the tube of the scope, then just the edges of the ring are bearing against the tube. Make sure that the rings bear fully against the tube of the scope. Usually I'll mount the bottoms of the rings and lay the scope into them and see if it will freely rotate along the axis of the scope in the ring bottoms. If it "grabs" in the rings, that is usually an indication that one of the rings is canted or misaligned with the tube and needs adjustment. Avoid placing anything inside the ring that will reduce its diameter unless it is supplied with the ring. If you put shims inside a ring that is not intended for use with them, the reduced diameter may dent the tube of the scope when tightened. I've mounted probably over a thousand scopes and can't remember any problems if the rings were square and torqued properly. That includes 416's, 50bmg's and others I don't remember. If you're around Fairbanks, I'd be happy to give you some pointers in person.
I did do this when I mounted the rings to the rail. I had no obvious alignment issues.
 

RigPig

New Hide Member
Jan 30, 2018
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#21
Hmm.

The scope should not be sliding, obviously. The equipment your using looks fine and that is not even a particularly hard recoiling caliber.
I do loath the lock-tight though. Lock tight tends to make things inconsistent.

For what it is worth I make sure the scope and inside of the rings are dry and clean and that the cap screws are greased. Greased cap screws do actually provide more force than dry but I do it for the consistency of the load they apply. I have never had a problem @ 20 inch lbs with this procedure.

I agree with your thoughts that lapping is not something that is nessecarry with quality stuff nowdays. My thought is that the locktight is causing you to get a poor read on how much load you are actually applying and probably also making that load uneven. My only other thought is that your ring tops might be canted to one side or the other and not showing the same gap between top and bottom on both sides.
Loctite in liquid form shouldn’t hinder the screws being tightened. I also checked the gap on each side with feeler gauges. As a former machinist, I’m picky about such things.
 
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