Searched for what I thought would be a topic that would've been covered by now, didn't find it.

I have a SAM7R-51. I bought an Arsenal side rail. I haven't successfully zeroed it yet (using an H2), but I'm wondering if maybe it's not dead center and if that's my problem. I'm not trying to use this rifle long distance, my plan is to zero it at 100 and use it for shots out to as far as maybe 200 or 250, minute of man is what I'm looking for. Is that a realistic goal with an off center optic?

Horizontal displacement is not a problem.
Let's say it's totally out of whack and a full 1/2 inch off to the left as mounted on your rifle.  So long as that 1/2 inch is parallel to the bore it will be 1/2" off at the muzzle, 1/2" of at 100 yards, and 1/2" off at 300 yards.  No problem.

It it's at an angle, that is definitely a problem.

my old ROMAK base is a bit tilted.



years ago, I tried to fit a M.I. mount, and it went downhill fast...literally

like this one...

Is that rail canted downward?

yes-skiovic

I've got one go the PK-AS optics that's mounted off center deliberately. The angle that it's off is so small that it doesn't really affect things out to 300 yards when zeroed at 200.

Have you checked that all the mounting points are tight?

AJ

On a psl that I had years back, the rail on the receiver was bent in at the front and it made it so I wasn't able to zero and optic that was mounted on it.  Once the rail was bent back into place it was fine.