Scope rail bedding 'WTF?'

[memilanuk]

So... factory rifle (Sav 10BA) that I've had for a while. Long story short, it's one of those guns that's always been a thorn in my side for one reason or another. Last year, after putting a new (NSS/Criterion) pre-fit barrel on it, I realized the scope rail was loose - again. Figured I'd fix that thing, once and for all. Got the JB weld out, and proceeded to (intentionally) permanently bed the rail (Farrell steel 20 moa) to the receiver. Cleaned it up, and let it sit to cure. Later, I was a little afraid that I maybe didn't get enough release agent on the screw threads and/or in the holes in the receiver, because I couldn't loosen the screws. Ah, well. The damned thing was glued down tight, done.

Except... the gun continued to disappoint. Couldn't find a load that worked. Imagine if you will, a 20" .308 Win that doesn't appear to like Berger 175 BTs, IMR 4064, Lapua brass or 210M primers - might break 1 moa on a good day. Weird, right? Checked action screws, swapped scopes, etc. Nada. Out of desperation, I tried some FGMM S175MK factory ammo. A *little* better, maybe. Borrowed a different chassis from a friend, and tried it again with some Berger factory 185 OTM ammo. First group was good, easy half moa. And it went downhill from there. 1.25-1.75 moa, two-group, shotgun pattern, stringing, etc.

Got it home, debating WTF to try next. Took the scope off, put it on the shelf. Took the chassis off to take back to it's owner. On a whim, I grabbed a torx key, and tried the rail screws. I mean, it sure *shot* like something was loose. And... while none of the screws were exactly 'loose', they sure as $hit weren't what I'd call tight, either. And they *all* came out, vs. before when two of them wouldn't turn at all. The rail was still on there, wouldn't come off with finger / hand pressure. Grabbed a small 8 oz ball peen and tapped the back of the rail and... it slid right off.

So now I've got a receiver with JB Weld residue on top, and a steel scope rail with JB Weld residue on the bottom, and no bleedin' idea how in the flying f$ck that joint came loose like that. The gun was either in the safe (most of the time) or in a case to and from the range. It wasn't exactly left out exposed to hot/cold or chemicals or anything that should have loosened the bond.

I guess my questions are a) best way to remove the remaining residue without (further) damaging anything, and b) ideas as to what might have gone wrong with the previous bedding attempt that it failed like this? Bad batch, bad mix, something else?

 

[Darryle]

Find a dealer who has the ability to media blast with soft plastic media, short of that, elbow grease in small delicate amounts.

Sounds like the JB Weld was bad

 

[memilanuk]

Would heat make it any easier to get off? Or just more likely to smear around and make more of a mess?

 

[AllenOne1]

If you can heat it up above 600 degrees it should come off. A heat gun/propane torch and razor blades come to mind. Any thick areas you could remove with a file prior to heating.

This issue of the scope base coming loose is exactly why a requirement for my current action was to have an integrated rail and lug. Two less headaches.

 

[hlee]

I’m not confident that JB weld is really that good at resisting shock. Under recoil, you have a firearm rapidly accelerating to the rear, and a relatively heavy scope resisting that movement. It’s the screws holding the rail to the receiver, and perhaps a lug on the rail, that allow the gun and scope to move as a unit.

There’s one (currently banned) member here that regularly uses JB weld to bed rails to receivers, but I’m pretty sure he’s actively avoiding using the JB weld as an adhesive for the rail. And, he’s something like 5 for 5 in buying Bergara rifles that have accuracy problems that are totally not a function of his scope bedding…

 

[diggler1833]

The last question of the OP makes me wonder what the metal prep was before applying the compound? Even though it is JB Weld, if there is just a touch of residual oil on there ... it'll create sub-optimal bonding.

 

[cas6969]

(Are they blind holes? Are your screws too long?)

 

[memilanuk]

(Are they blind holes? Are your screws too long?)

No, and no.

 

[memilanuk]

The last question of the OP makes me wonder what the metal prep was before applying the compound? Even though it is JB Weld, if there is just a touch of residual oil on there ... it'll create sub-optimal bonding.

TBH, it was over a year ago, so I don't really recall what all I did as far as prep. FWIW, the JB seems to have stuck okay to the rail, and to the receiver - hence the need to get it off of those. It's the material in between that didn't appear to hold. Seems like it'd be odd for the stuff in the middle to be contaminated, but not what was touching either surface? Not saying it couldn't / didn't happen that way, but it sounds bizarre.

 

[memilanuk]

I’m not confident that JB weld is really that good at resisting shock. Under recoil, you have a firearm rapidly accelerating to the rear, and a relatively heavy scope resisting that movement. It’s the screws holding the rail to the receiver, and perhaps a lug on the rail, that allow the gun and scope to move as a unit.

There’s one (currently banned) member here that regularly uses JB weld to bed rails to receivers, but I’m pretty sure he’s actively avoiding using the JB weld as an adhesive for the rail. And, he’s something like 5 for 5 in buying Bergara rifles that have accuracy problems that are totally not a function of his scope bedding…

You mean that guy that has his own "Where's Waldo" thread over in the Pit?

Yeah, I think next time around I'm going to spring for the good stuff... either Devcon or MarineTex.

 

[memilanuk]

This issue of the scope base coming loose is exactly why a requirement for my current action was to have an integrated rail

Eh... I've only ever really had the issue with a couple (of more than a few) factory actions - this being one of them. My Bighorn Origin, for instance, has way more rounds through it than this thing, and the rail has never came loose (yet, probably will now!). But yeah, I hear ya. That's part of why I have an Aero Solus on order - integral rail, lug, comes with trigger hanger (I had a MF of a time getting a trigger set up on the Origin), and AIAW mag cuts - for less $$$. I do love the mechanical ejector and CRF on the Origin, though.

 

[6.5SH]

Rather than try to glue it on, use it as bedding to fill gaps as is the usual case. Have the receiver drilled and re-tapped for #8 machine screws, given the repeated issue I'm guessing the current hole(s) are slightly oversize or out of round.
It also looks like the Farrell base doesn't have a recoil lug, if there is enough meat there a set screw could be installed on the underside of the base.

 

[6brshooter]

Had a buddy that had a rail constantly coming loose on his savage. I gave him he'll for not getting threads in action and screw decreased. Turns out it was shitty loctite, a new bottle cured it. When I had savages, I always ran a badger rail with recoil lug. Does the farrel have that?

 

[ma smith]

ideas as to what might have gone wrong with the previous bedding attempt that it failed like this?

any type of surface contamination or a poor surface prep will do this.

ETA -

Also, epoxy has very weak sheer strength, so it needs a thicker (vs thinner) layer to tolerate a high-shearing-force like sideways hammer blow. But a normal rail,since its not designed for it, may not have clearance for this bonding layer to fit between the action and the rail,

TLDR you are possibly using a combination of part designs, adhesive, and surface prep which is not ideal.

 

[supercorndogs]

I’m not confident that JB weld is really that good at resisting shock. Under recoil, you have a firearm rapidly accelerating to the rear, and a relatively heavy scope resisting that movement. It’s the screws holding the rail to the receiver, and perhaps a lug on the rail, that allow the gun and scope to move as a unit.

There’s one (currently banned) member here that regularly uses JB weld to bed rails to receivers, but I’m pretty sure he’s actively avoiding using the JB weld as an adhesive for the rail. And, he’s something like 5 for 5 in buying Bergara rifles that have accuracy problems that are totally not a function of his scope bedding…

The screws don't stop the base from moving. The friction from clamping is what holds things in place.

Bedding basses is pretty common practice on production actions. It's usually worth checking. If you tighten the screws on one end, does it make a gap on the other?

The actions I have seen that really needed base bedding also needed tang bedding to shoot well in a chassis.

So if we are trying to relive stress on the base from tolerance stacking or a hump backed action putting epoxy under it and tightening it down isn't going to relive that stress.

 

[ma smith]

The way to think about bedding can vary a bit by intent. Are you tring to glue the thing on?

Not really, and this is proably a bad idea...

Mainly what you are trying to do is create inertial resistance, ie to prevent mobility of the part assembly. This is much closer to the design intent of wheel chocks...eg

In ths case, the bedding will help prevent any small pre-cursor movements to might lead up to loosening of the fasteners, but the fasteners/friction fit still does all the real work. You need a square, well designed, and properly made part for this.

 

[Makinchips208]

Wire feed the steel rail to the receiver?

It is a savage after all.

 

[7mm-08 Freak]

Wire feed the steel rail to the receiver?

It is a savage after all.

SOAB JB Weld on a scope rail? Even on a Savage that's some real Booty fab right there! Might as well stick weld it on. Its not worth a TIG job

 

[MikeMiller]

Monte the secrets to bed/gluing base to receiver 1. Acetone base and top of receiver
2. Mix JB well
3. Provide good layer
4. Don’t get screws very tight
5. Wipe excess with acetone
6. Let dry 48 hrs

Once 48 hrs is up the only way off is heat
I have never had one shear or come loose doing that

Also propane touch will get the stuff on rec loose

 

[hlee]

The screws don't stop the base from moving. The friction from clamping is what holds things in place.

Yeah, we’re on the same page. I didn’t want to run down a big scientific rabbit hole, but it is the screws applying the normal force that creates the friction. So, the screws hold the thing in place…

 

[memilanuk]

Monte the secrets to bed/gluing base to receiver 1. Acetone base and top of receiver
2. Mix JB well
3. Provide good layer
4. Don’t get screws very tight
5. Wipe excess with acetone
6. Let dry 48 hrs

Once 48 hrs is up the only way off is heat
I have never had one shear or come loose doing that

Also propane touch will get the stuff on rec loose

Hey Mike. Long time no see. Hopefully you're getting dried out down there

I remember when you first told me about this stuff; I had that one 12 FTR that shot amazing (lost count of the medals that thing brought home) but the damn rail would come loose somewhere around 12-18 months - usually at the worst possible time. IIRC I chickened out and put some release agent on the receiver on that one... but it's never came loose since.

 

[memilanuk]

The actions I have seen that really needed base bedding also needed tang bedding to shoot well in a chassis.

So if we are trying to relive stress on the base from tolerance stacking or a hump backed action putting epoxy under it and tightening it down isn't going to relive that stress.

Once I get this thing cleaned up, I'm probably going to (re)bed the rail *and* the chassis (MDT LSS-XL). One of my multitude of winter projects...

 

[JoshPutman]

 

[hlee]

View attachment 8555164

Smiff. Gunsmiff.

 

[tekmann2377]

Another option would be to use another compound for bedding that is actually bedding compound. Loctite 660 is exactly that and is designed for bedding loose or worn metal parts in rotating assemblies. It is also removable with the appropriate (albeit rare) solvent. I have used it with good success.

 

[supercorndogs]

660 is not a bedding compound. Gap fill is .01-.02.

LOCTITE® 660

High strength, large gap-filling for bonding cylindrical parts

www.henkel-adhesives.com