I recently brought a new scope for a rifle I had built. When getting ready to mount the scope I checked the receiver with a straight edge. It is not level. I am wondering what is the best way to approach installing the scope, rings and bases? I would like to stick to Talleys or Leupold Dual Dovetails or Backcountry rings. But, I have not ruled out the DNZ Game Reaper one piece.

This is a rifle for hunting and plinking. Mild caliber—6.5x257R. Do I install the bases to the receiver incline and the lap and bed the rings? Or, do I level out the base and bed with epoxy by tightening the rear screw, letting the front of the base free float? The lap the rings or bed?


How would you approach this issue. Any advice is appreciated. Thanks.

How do you know that one base isn't taller than the other? There are plenty of rifles with different height bases.

If I am understanding the question, I mounted a set of Talleys and the ran the straight edge flat with the bottom of the rear base and it was not touching the front mount. There was still a small gap. I didn’t measure it with a feeler gauge, but there is definitely a height difference.

The base would have to be cut at angle rather than flat to make up the difference. In the large picture the straight edge contacts the receiver in the rear for both mounts, but has a gap where the front screw is located.

I have a set of dual dovetail bases. I will check the front/rear thickness with my micrometer to see if they are the same or different. It could be the aluminum Talleys that are to conform the to receiver when torqued down.

Front dual dovetail mount was same thickness front to back. Since the angle of the receiver is almost the same back to front, probably lapping is the best choice. Unless someone else has a better idea.

if that is a M700

front base is 0.147 thick
rear base is 0.272 thick

is the front to back difference 0.125 (1/8)

AFTER installing bases, confirm flatness.

If STILL is not true, then use Burris Zee rings w plastic inserts to correct the misalignment

Use a pic rail and bed it into a liquid shim of JB Weld. Use only the inside 2 screws just barely snug until the epoxy cures.

There are two ways you can do the job that work well. One requires more tooling than the other. If you want two piece bases, you will need a straight rod (think ring lap) that can be used to establish the rear base height when all parts are assembled. You can then bed the rear base to correct the height difference. The better/easier alternative is to use a one piece base and bed the rear of it to the receiver when the front of the base is tight to the front ring of the receiver. Do not bed the front of either base to the front ring of the receiver to correct any angular issues. The front ring determines where the barrel is pointed, so if you bed to correct the angle at the front ring that you illustrated in your photos your rifle will shoot low to the point that it may be outside the adjustment range of the scope. Whether you choose a one piece base or two piece, the rear needs to be bedded or the height difference will put the scope tube under a huge stress if not bedded to be straight and stress free.

Thanks all good suggestions.

BangPop: do you think a 30mm aluminum or carbon fiber bar would be light enough to support the rings and base for using two piece mounts? I have the lapping bar but am worried about weight and inducing stress to the mount when tightened down and not supported by the front.

The DNZ mount would work the same as a pic rail I would assume. Probably a lot less work than trying the two piece route. Pic rail is plan B I guess.

Interesting, I need help with a gun....no make or model, might as well be, I need help with the air. Obviously the front and rear action rings are not level under that streight edge, so they are not the same height, if square. A scope base or bases should be level and centered to the axis of the bore as mounted.
First thing you need are bases or a base for that make and model action. Forget shims or Fouxinh up a scope mount job wih epoxy.

Use the lap and stand the rifle up vertically so gravity has no ability to flex the parts.

And if the base, or bases that are for that action don't fit correctly, then what.........?

Why not use brass shims instead of epoxy. (soda pop can material for shimming works also) You should be able to lay your straight edge along the front of the receiver and use feeler gauge to determine how much shimming you need. A lot more forgiving when setting it up than epoxy.

Is shim stock used to get a close fit when bedding a rifle, or is epoxy used to get an exact molded fit of the two surfaces that need to mate? Shim stock will get close, but bedding with epoxy will be a mirror image.

I have shimmed three different scope mounts in the past, 7 mm Weatherby mag, 30-06 and.308. All worked fine. You can get within .002-.003 measuring with feeler gauge. Of course you need a good set of calipers or micrometer and a range of shim stock. How much does epoxy shrink and how impervious is it to cleaning products? Not saying it is the only way, just another way that works. Plus you can add more, remove some, or whatever. Pretty hard to do with epoxy. Since the OP has the lapping jig, it should be easier yet.

Back when rifle scopes did not have self centering cross hairs, it was a conventional way to get you scope within the adjustable range of it.

Another thought is what about the recent thread about bedding compounds/epoxies deteriorating in time?

Then you modify the bases: Get them as close as humanly possible, then glass bed them to the receiver. Rough up the bottom of the bases, and use release agent on the receiver. That way the epoxy is on the bases, and the bases are fit for that rifle/receiver. After that, you shouldn't even need to lap the rings. Pretty simple, and no I would not use soda pop cans or any other kind of shim.

Have you ever tried shims? I bet not. You could use soda pop material, IF and that is big if, you could find the right thickness which is why I advised brass shim stock in different thicknesses. And no I would not use epoxy. That is about like using a dremel tool for fine metal or stock work.

Maybe the OP has no way to modify the bases.

Another thought is what about the recent thread about bedding compounds/epoxies deteriorating in time?

On the Weatherby 7 mag I did, Weatherby advised using a Remington 700 base along with a shim as the front of the receiver was higher than the back and there was no correct fitting bases on the market.

Burris markets off set scope rings for the same problem for misaligned scope bases.

https://www.burrisoptics.com/mounting-systems/signature-rings

In Brownell's Gunsmith Kinks I, page 186 there is a short article about using Chevy main bearing shims for the fix

First, put your straight edge flat on the front of the receiver letting the straight edge go over the rear of the receiver. I suspect that you will find that the front and the rear of the receiver are parallel. Not the same height but parallel. Measure the difference between the bottom of the straight edge and the top of the rear of the receiver. That will be the difference in base height. The receiver sure looks like a Remington or clone and as pointed out the bases are different height.

[quote=Rapier]

Nonsense. Bed the bases!

That makes sense. Thanks. Yes R700 long action for those that have questioned it.

This would be what I would do if it was mine.

You cannot lap that problem out. You may get the rings circular by lapping the hell out of them, but it will be nowhere near parallel to the rifle bore. And there will not be enough adjustment in a scope to fix that. A taller rear base is in order. Being a r700 this is a no brainer…

Exactly. Do like I said and problem solved. There are not a lot of "gunsmiths" here obviously.. This chiidt isn't that hard to understand. Guys want to make it harder than it is.

BTDT a couple times, and no, I don't use soda pop cans..

Before:


After: Fine tuning the bases:


When you get the base fairly close:

Those were pretty close, but fit by hand. The next step is to epoxy bed the bases...
If you use an alignment bar, you won't even need to lap the rings.

Some of you guys are way overthinking this. Of course, I'm not a "gunsmith"... YMMV..

After starting with the correct bases/ring mounts for the action, they need to be made level with each other. Bedding the bases can accomplish this (if done correctly). It also mates the bases perfectly to that particular action...just like bedding and action into a stock. At that point, the bases and action should be considered 'as one'. Once that's done, the final part is lapping the rings and/or bedding the rings for maximum contact. If using the Burris Signature rings with the inserts, the inserts will conform to the scope tube the same as bedding does.

Good shootin' -Al