Gunsmithing scope base bedding

[Twitch2120]

I'm sure the topic has been beat to death but I have a specific question about my setup. I've placed my 20moa badger rail on my aac-sd. Torqued the front and there is almost zero play. I might be able to stick a .001 feeler into the gap. torque the back and its the same story on the front. Very little discernible movement when pressed. my question is if I should try bedding the entire rail, just one end or just say screw it, I'm making it a bigger deal than its worth. If bedding is the way to go should I put down a film of grease or oil to prevent any rusting under the base or just run it and check once every blue moon.

Thanks!

 

[Beef82]

Re: scope base bedding

It doesn't sound as though you need to bed the base. If there's discernable play or a definite gap the base will distort some when torqued down, enough to matter? that's your call. If you elect to bed it, do the whole thing.
As far as corrosion clean and lightly oil the top of the receiver as you would normally before final assembly and corrosion should not be a problem.

 

[Greg Langelius *]

Re: scope base bedding

Play is play.

The physics of the situation say that when the parts are mated, stresses are shared between both parts.

If that's important to you, bed the bases.

After that, remove and clean the contact zones, and establish rust protection between the parts.

Unless both parts are made of identical materials, bimetallic corrosion is a real possibility. I've has it bad enough on my own rifles to require some pricey repair. I went with Cerakote, and I no longer have that worry.

Greg

 

[Deadshot2]

Re: scope base bedding

Some, myself among them, bed every scope mount, period. No matter how good the mount, there will be differences in tolerances from one shop to another, from heat treating and polishing of the action, etc.

I don't even bother with any parting agent when I bed the mounts with Devcon 10110. I want the tightest, strongest bond possible with no movement or stress on the mounting screws. I do "wax" the screws so I can remove them if I ever want to remove the mount then heat the mount to break the bond of the base to the action. Just how many times does one change a scope base? Usually just the scope and rings, not the base.

No more having to take the scope off and re-torque the base screws just to make sure they haven't shot loose.

For those that don't think the idea of a semi-permanent bond is all that great, just wipe the action with mineral spirits and let dry. That will allow for some parting action yet still let the epoxy be as close as possible to the action surface.

 

[highridge1]

Re: scope base bedding

I would bed the base unless the fit was near perfect.

 

[LRI]

Re: scope base bedding

Your tiny gap could very likely be the result of the base distorting from the machine work performed on it during manufacturing. Often the case with a long/skinny part.

Its not uncommon at all for a piece of material to "bananna" once its removed from a machine vise.

You can bed it if you like. Ive never done it personally. Instead I wrap the receiver with emery cloth and use it to lap in the base. That's if the action is coated and I don't want to do it over. If its not ill smear 100 grit on the receiver and "rub one out" to fit it.

Good luck.

C.

 

[Jkob]

Re: scope base bedding

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Twitch2120</div><div class="ubbcode-body">I'm sure the topic has been beat to death but I have a specific question about my setup. I've placed my 20moa badger rail on my aac-sd. Torqued the front and there is almost zero play. I might be able to stick a .001 feeler into the gap. torque the back and its the same story on the front. Very little discernible movement when pressed. my question is if I should try bedding the entire rail, just one end or just say screw it, I'm making it a bigger deal than its worth. If bedding is the way to go should I put down a film of grease or oil to prevent any rusting under the base or just run it and check once every blue moon.

Thanks! </div></div>

When you tighten down the base, the torque you put on the screws is enough to align the base to the receiver. what you really need to do is to bed theescope to the rings. This will ensure there is not any torque to distort the scope.

Jim

 

[Deadshot2]

Re: scope base bedding

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body"> Instead I wrap the receiver with emery cloth and use it to lap in the base. That's if the action is coated and I don't want to do it over. If its not ill smear 100 grit on the receiver and "rub one out" to fit it.

Good luck.

C. </div></div>

Using the emery cloth gives you a different radius on the base than that of the action. It's off by the thickness of the emery cloth. Would be better, if you don't want to mar the action, to merely use prussian blue and fit the base just like inletting a stock. Just scrape off he points that "mark" until the entire base "marks".

 

[E. Bryant]

Re: scope base bedding

If the base is close-but-not-perfect, I lap it to the receiver with 240 grit Clover compound. Put some grease, thick oil, or anti-seize between the base and receiver to inhibit corrosion.

 

[LRI]

Re: scope base bedding

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Deadshot2</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body"> Instead I wrap the receiver with emery cloth and use it to lap in the base. That's if the action is coated and I don't want to do it over. If its not ill smear 100 grit on the receiver and "rub one out" to fit it.

Good luck.

C. </div></div>

Using the emery cloth gives you a different radius on the base than that of the action. It's off by the thickness of the emery cloth. Would be better, if you don't want to mar the action, to merely use prussian blue and fit the base just like inletting a stock. Just scrape off he points that "mark" until the entire base "marks". </div></div>


In theory, yes. Absolutely right.

In practice, it don't amount to one turd of difference.

Mathematics and the real world often collide with one another.

Case in point:

It's amusing how one will go to the ends of the earth to fit a scope base because every sacred cow in gun land says it has to be that way. Yet not one person on this site has yet to ever talk/inquire about lappin in the bottom of a guard screw head to the floor metal to ensure peripheral contact, ensured the angle of the chamfer on the guard metal is square to the screw head, or even made sure the holes are on the same center to center location as the receiver.

Be your own judge/jury. What's going to have more influence? A base that's off by .01" over a 5-8 inch span or a guard screw binding .01-.03 and failing to obtain an even/concentric purchase on the floor metal?

Which is more likely to twist an action up in the stock?

Check it once. Fix it, and then tell me how much difference it feels when you tighten everything up.

That sort of stuff means a great deal more to me than fretting over a few theoretical .001's of base/receiver fit. If it's really that big of a deal then how in the world does the receiver successfully support a 7-9lb barrel dangling 20-30 inches off the end of it? -Yet it can't possibly shoot well if a 3/8" thick scope base (often made from AL) isn't fitted perfectly "dead" to the receiver?

Really??

Please understand this isn't a personal attack directed towards you. It's just that your question sparked a response that I've been chewing on the last several months when this sort of topic comes up.



C

 

[Deadshot2]

Re: scope base bedding

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body"> If it's really that big of a deal then how in the world does the receiver successfully support a 7-9lb barrel dangling 20-30 inches off the end of it? -Yet it can't possibly shoot well if a 3/8" thick scope base (often made from AL) isn't fitted perfectly "dead" to the receiver?

</div></div>

If it doesn't fit, the chances of moving under recoil or through heating/cooling of the metals are greater. How much does that .001" at a scope base mean at 1,000 yards?

Everyone has their own way of doing things and has their own list of "That doesn't matter" items.

As for an aluminum scope rail/base? Not on any of my rifles.

 

[Jackem]

Re: scope base bedding


I used an aluminum rail, made sure it fit the action with no play, by feel at least. I then coated the bottom of the rail with blue Locktite and torqued the screws.

The rail is electrically isolated and bedded but still removable, no?

 

[LRI]

Re: scope base bedding

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Deadshot2</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body"> If it's really that big of a deal then how in the world does the receiver successfully support a 7-9lb barrel dangling 20-30 inches off the end of it? -Yet it can't possibly shoot well if a 3/8" thick scope base (often made from AL) isn't fitted perfectly "dead" to the receiver?

</div></div>

If it doesn't fit, the chances of moving under recoil or through heating/cooling of the metals are greater. How much does that .001" at a scope base mean at 1,000 yards?

Everyone has their own way of doing things and has their own list of "That doesn't matter" items.

As for an aluminum scope rail/base? Not on any of my rifles. </div></div>


And the temperature difference between a base/receiver is???

Measured how???

Now consider the convection differences between the two materials.

Maybe its the base being heated and then transferring to the rings, causing the scope to heat up, which then creates a mirage inside the tube of the scope?

What the hell right? I mean, lets perpetuate the lunacy.

 

[hero's machine]

Re: scope base bedding

You gotta love gun plumbing....mix equal parts machinist, auto mechanic, carpenter, quasi-nasa engineer and English major....lol.

 

[Deadshot2]

Re: scope base bedding

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: hero's machine</div><div class="ubbcode-body">You gotta love gun plumbing....mix equal parts machinist, auto mechanic, carpenter, quasi-nasa engineer and English major....lol. </div></div>

You left out Philosopher and Gypsy Fortune Teller

 

[Beef82]

Re: scope base bedding

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body">
It's amusing how one will go to the ends of the earth to fit a scope base because every sacred cow in gun land says it has to be that way. Yet not one person on this site has yet to ever talk/inquire about lappin in the bottom of a guard screw head to the floor metal to ensure peripheral contact, ensured the angle of the chamfer on the guard metal is square to the screw head, or even made sure the holes are on the same center to center location as the receiver.

Be your own judge/jury. What's going to have more influence? A base that's off by .01" over a 5-8 inch span or a guard screw binding .01-.03 and failing to obtain an even/concentric purchase on the floor metal?

Which is more likely to twist an action up in the stock?

Check it once. Fix it, and then tell me how much difference it feels when you tighten everything up.

That sort of stuff means a great deal more to me than fretting over a few theoretical .001's of base/receiver fit. If it's really that big of a deal then how in the world does the receiver successfully support a 7-9lb barrel dangling 20-30 inches off the end of it? -Yet it can't possibly shoot well if a 3/8" thick scope base (often made from AL) isn't fitted perfectly "dead" to the receiver?

Really??

Please understand this isn't a personal attack directed towards you. It's just that your question sparked a response that I've been chewing on the last several months when this sort of topic comes up.



C </div></div>

Great, now instead of do I need to? what compound do I use to? or how do I? bed my rail, its gonna be, how do I bed/lap my rail perfectly centered and inline with the bore? How do I determine if its square to the horizontal plane of the bore? Do I need to lap in the mounting screws? What's the best compound to lap the action screws? Will it work on the rail screws too? How can I be sure the BM is square to the horizontal plane of the receiver? Does lapping the action screws change what I should torque them too? I got a new stock, do I need to lap my action screws again? Is this stuff availible at Lowes? All I have is a tape measure, bubble level, ball peen, screwdriver and allen key, but they're Kobalt so they're good, do I need anything else?

Way to open a can of worms. Joking, sort of.

 

[Twitch2120]

Re: scope base bedding

MacGyver could do it without the level.

 

[300sniper]

Re: scope base bedding

know what i would do if i "might be able to might be able to stick a .001 feeler into the gap" when one end of the base was screwed down? i'd screw down the other side and shoot the damn thing without even worrying about it. none of my aftermarket bases are bedded on remington receivers. i've never missed a shot and said to myself "damn, i wish i had bedded the base".

 

[bobbye]

Re: scope base bedding

Does it hurt to bed a rail? Can it hurt not to bed a rail?
Why take a chance?

 

[Greg Langelius *]

Re: scope base bedding

I think it's a binary issue. You either have a gap or you don't. If you do; you fix it, period.

Greg

 

[E. Bryant]

Re: scope base bedding

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Greg Langelius *</div><div class="ubbcode-body">I think it's a binary issue. You either have a gap or you don't.</div></div>

There will always be a gap. The question comes down to how large of a gap is tolerable, and what the "fix" does to the relationship between the mount and the rest of the system. If you reduce the gap between the receiver and the mount, but end up worsening the alignment between the mount and the barrel bore in the process, have you really made things better?

A few moments of idle thought on this Monday morning has me believing that rotation of the mount about the X-axis (the axis parallel to the bore) would be quite bad, since it will be magnified by the scope/bore distance to create a potentially ugly offset that cannot be taken up by adjustment of the scope knobs. Rotation of the mount about the Z-axis (the vertical axis) is substantially less problematic, since it can be taken up to a reasonable extent by scope windage adjustments. Without the use of a fixture to guide lapping or bedding operations, this sort of misalignment is pretty hard to avoid.

Does any of this help address the original question? It does not for me; all it does is make me want to replace every action I own with a Surgeon.

 

[LRI]

Re: scope base bedding

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 300sniper</div><div class="ubbcode-body">know what i would do if i "might be able to might be able to stick a .001 feeler into the gap" when one end of the base was screwed down? i'd screw down the other side and shoot the damn thing without even worrying about it. none of my aftermarket bases are bedded on remington receivers. i've never missed a shot and said to myself "damn, i wish i had bedded the base". </div></div>


Whut HE SAID!



Here's my issue with it. It goes along the same lines as skin bedding a receiver.

Mix up a batch of your favorite bedding compound. Wall spackle or unobtanium used on the plasma reactor at NASA. Your choice.

Spread it out paper thin on a prepared surface. Thin, thin, thin.

Now spread out a thicker layer.

Let them both cure overnight.


Now tap on the thin stuff with a ball peen hammer. How long does it take before it starts lifting from the substrate? (surface its supposed to be bonded to)

Now tap on the thicker stuff. How much more tolerant is it to the impact forces?

Translate all this blunt force trauma to what a gun typically sees. If its a field duty gun, it's going to be dropped, it'll be banged around. Then there's recoil. Solvent contamination from cleaning/lubricating.

All of this in my little brain translates into alot of work that in the end only fools yourself. In 13 years I've yet to see a bedded base that didn't have some form of erosion present when I took it off the receiver.

If it's lapped, then you take the "murph factor" out of the equation. Understand I don't do this because I have a die hard religious conviction that it actually does anything. I do it because if I DON'T then clients go from "zero to high maintenance" in short order because they believe its important.

I have a fixture that I made for this. Judging by the response I'm betting you don't. I don't have the tools, nor do I even know where to begin when it comes to overhauling an automatic transmission. You might have 20+ years experience at it with all the specialty tools sitting in a shiny Snap On box.

I suggest this:

Bolt it on and go shoot it. Shoot the snot out of it. At least a 100 rounds.

Peel it off and bed it. Then go shoot another 100 rounds.


Compare your plot sheets and see what you find out. As Bert eluded to, you'll likely find that all you did was devote a half hour to playing gun tinker at your bench instead of making bullets and/or becoming a better shot.


C.

 

[E. Bryant]

Re: scope base bedding

Devcon calls for a <span style="font-style: italic">minimum</span> thickness of 3-5 mils for their Steel Putty, and almost anyone who has used the stuff would say that this is way too thin.