Canted Scope Mount

alseides said:

I just noticed that the ARMS 18 mount I have on my SAI M1A Loaded is canted to the left. When looking from the rear, the right edge is higher than the left.

This mount came with the rifle and I haven't noticed this before. I have mainly been shooting with iron sights and when I look through the channel on the mount, I can see the sights just fine. The only things I have done with the mount was to make sure the side screw on the receiver was secure and the set screw in the stripper clip dovetail was secured with Loc-Tite. I have not pulled it off and re-mounted it. The angle of cant is not profound but it is noticeable.

I am guessing that this is probably not that big of an issue. As long as I can set a scope in its rings with the cross hairs level, it should still work fine, right?

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Do you have torque specs for the mount and install instructions? I'd suggest removing the scope mount and starting off from the beginning. Never assume the previous owner knew what he was doing unless you absolutely trust them.

Eagle7840 said:

Do you have torque specs for the mount and install instructions? I'd suggest removing the scope mount and starting off from the beginning. Never assume the previous owner knew what he was doing unless you absolutely trust them.

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I pulled the mount off to try to figure out the problem. When I can get the rail level, the side mounting screw does not line up with the screw hole in the side of the receiver. If I get the screw lined up, the rail cants again. I am beginning to think it was always this way but somehow I never noticed.

I did not mess with the front contact screw. I'll try raising that and seeing if that helps with the fit but I don't think it will.

Receiver might be ever so slightly out of spec, mount could be out of spec, maybe both? IMHO as long as the mount isn't bending when fully torqued down I would just put the scope on it. Might be a good idea to lapp the rings first though.

edit: whatever you do don't overtorque anything, you can strip the screws etc.

alseides said:

I pulled the mount off to try to figure out the problem. When I can get the rail level, the side mounting screw does not line up with the screw hole in the side of the receiver. If I get the screw lined up, the rail cants again. I am beginning to think it was always this way but somehow I never noticed.

I did not mess with the front contact screw. I'll try raising that and seeing if that helps with the fit but I don't think it will.

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Try removing all tension and contact points of the leveling screws and then install the scope mount but only finger tighten the receiver mount bolt. Then try leveling the base front to rear and then torquing the receiver mount bolt to spec. Becareful so not to overdo it if you feel any resistance on the receiver bolt and strip any threads on the receiver. I'm guessing you have an out of spec scope base causing your problems and would replace it with a Bassett or Sadlak mount. Both have had very good reviews here and I went with the Bassett mount because of the quick interchange from scope to irons.

My ARMS-18 mount had some interference with the receiver.
Loosen the fore and aft set screws. Install the mount finger tight. Use a narrow strip of paper: check the gap between mount and receiver all the way around. The mount should touch only on the alignment keys before you tighten the set screws.

Download the instructions, which are difficult to read. Follow the sequence.

I loosened all the screws, the side, dovetail, and front set screws. I also retracted the front torsion pad until it was flush with the underside of the rail. After a lot of alignment adjustments, wiggling around, and close eyeballing, I can only get the rail level when I do not have the side screw threaded in. Once I start hand tightening the side screw the rail begins canting. I've fiddled with the mount so that the cant is not as pronounced but it is still there. I need to dig out my level to double check but I am quite certain it isn't level. I find it a bit odd that the cant is easier to see from the muzzle end instead of from the rear.

I think the small degree of cant has always been there, I just never noticed. I am a bit disappointed, I had a scope and rings ready to go. If I end up getting a different mount, I'll most likely have to get different rings.

That cant is meaningless for optics function, between mounting the scope to where it "looks good" to your eyes as well as how you hold the rifle when shooting you probably cant it far more than that anyways. The only thing I would worry about is that once the screws are torqued down the mount flexes and your rings will no longer be perfectly in line with one another. Then you go mount your scope and bend it

Cant and level are secondary considerations after the keys are aligned in the grooves.

noob14s said:

That cant is meaningless for optics function, between mounting the scope to where it "looks good" to your eyes as well as how you hold the rifle when shooting you probably cant it far more than that anyways. The only thing I would worry about is that once the screws are torqued down the mount flexes and your rings will no longer be perfectly in line with one another. Then you go mount your scope and bend it

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I had thought that getting the mount level (Side-to-side and front to back) was one of the most important parts of mounting optics. A slight cant isn't a big problem? I'll try to post some photos to show what I am looking at. If this turns out to be a non-issue, I'll be thrilled.

alseides said:

I had thought that getting the mount level (Side-to-side and front to back) was one of the most important parts of mounting optics. A slight cant isn't a big problem? I'll try to post some photos to show what I am looking at. If this turns out to be a non-issue, I'll be thrilled.

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If the scope mount is canted slightly to the left then when you put the scope in the rings you cant it slightly to the right. Like I said be more worried about whether or not the mount is flexing when torqued down. You want the rings to be concentric with one another otherwise you can damage your scope.

The keys on the mount must fit into the grooves on the receiver. After solid installation, if there is a cant or misalignment of the scope with the bore, that situation can be addresed.
If the rings are misaligned too much to be corrected, perhaps the manufacturer would consider an exchange?

noob14s said:

The only thing I would worry about is that once the screws are torqued down the mount flexes and your rings will no longer be perfectly in line with one another.

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I consider that for every scope installation, whether rifle or slide-mounted pistol scope, and I lap my rings or use PosAlign inserts. Receivers are finished by hand, and bases and rings are not perfect. Lots of scopes are bent slightly by misaligned rings.

I have a arms 18 on my NM, it looks canted and off center but the scope lines up on target nice. I have more elevation and wind than I will ever use. Shoots out to 617 like a dream. If the scope lines up good and you have even wind and good elevation I would not worry about it to much. Just make sure the dovetail is good and tite. And do not over do the side bolt, you will strip it. I did it twice..... Stupid stupid!

I took some photos of the scope mount. Hopefully it is clear enough to show what I am talking about. Everything is only hand-tightened at this point. Please excuse the mess in the background and the cat.

On my ARMS18 I had to remove some material from the rear of the mount where it contacts the stripper clip guide mount. That was causing the mount to cant in the same direction as yours.

Now only the screw insert touches the guide mount. Lines up perfectly. I think one of our Gurus does this for the mounts he puts on. I don't use it anymore as I get too many Stovepipes.

Walnut Scout guessed my next question: Does the mount clear the dovetail for the stripper clip guide?
And, do you have a square to check the angle of the slotted base with the left side of the mount.
To me, your photos don't show a cant.

shooter86314 said:

Walnut Scout guessed my next question: Does the mount clear the dovetail for the stripper clip guide?
And, do you have a square to check the angle of the slotted base with the left side of the mount.
To me, your photos don't show a cant.

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Sorry, I'll need some clarification on the questions.

What is meant by the mount clearing the dovetail for the stripper clip guide?

Does slotted base refer to the groove at the bottom of the receiver?

After you torque the mounting screw on the left side, before you install the rear set screw, there should be a slight gap between the rear of the mount and the forward angled face of the dovetail slot. Then the two screws and dovetail insert should adjusted to be tight without bending the mount.

In pic #1 I see the cant clearly. Aiming off to the left. The dovetail in question is what I called the Stripper Clip guide mount. And in pic 2 and 3 I see no gap there which is what Shooter is referring to.

shooter86314 said:

After you torque the mounting screw on the left side, before you install the rear set screw, there should be a slight gap between the rear of the mount and the forward angled face of the dovetail slot. Then the two screws and dovetail insert should adjusted to be tight without bending the mount.

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I'll have to remove the set screw and the dovetail insert to re-check that. Or did you want me to leave the dovetail insert in? Also, I haven't torqued anything down yet, just finger tight. To properly check the gap, I need to torque down the side screw to the 90 ft-lbs required w/o the rear set screw in place?