I mounted a RS Regulate AK-301 side rail lower mount on my new M90 and notice that the rail when mounted properly, appears to cant slightly to the left.  I put the lower mount on my Zastava M70 and it looks exactly the same.

I checked the mount and it appears in spec.  When I look at both weapon's rails though, they look as if they are very slightly canted to the left when looking from the buttstock forward.  I have to assume Zastava did it for
a reason, they have been making guns for several decades now.  But why would it be like this?

Tolerances



Slight cant and off center on my M10, on the plus side RS Regulate has some adjustment. Kinda the Norm with AKs right? If it can still be zero'd it's fine. How bad is your cant?

If you look really close at an AK you will find certain parts aren't completely level. It's probably a nightmare for those with OCD. I just learned to accept it honestly.

Lots better than a PO or especially a Zrac.

I have an MI ring mount that does this on my M77. It appears that the angle of the dovetails on the rail don't totally match up with the surfaces on the mount, and while tightening the clamp wants to bind at the bottom before it has fully engaged the rail, which causes the top to shift outward,  and the whole thing then appears to be canted to the left.

It doesn't do this with any other AK rail, only the Yugo

I found that I needed to press the mount flat against the face of the rail when setting the initial clamp tension adjustment and thereafter whenever clamping it on. Then it will clamp down centered over the dust cover and zero is repeatable - I have carried the M77 in the woods two hunting seasons and never lost zero.

This is an AK style mount that I modded for the Yugo rail at a time when Yugo mounts were rare. I have not tried a newer Yugo specific mount, maybe the newer Yugo specific mounts from RS and MI don't have this issue.

I did get it to sit straight.  Simple solution to the problem too.  I applied a little crazy glue to the top mount rail, and the bottom mount rail, let them dry, then put it back on.  
This changed the angle to straight up and down, and now my sight is right where I want it to be, and no longer canted.