Disclaimer, I have no experience with either of these. I would think you’d be best served with a setup that mimics the height of the OEM sights. This would keep your cheek weld nearly the same. Lowering (and/or raising) the RD would require you to hold/shoot differently and may adversely effect your accuracy.
Upper mount vs. chassis? I’d mount to the receiver. Try both and determine which works better for you. Target acquisition, speed and accuracy are all important considerations.
Thanks @Dred and @Festus for your feedback. Will do the movement and will try. Saw another user’s video with the original Ruger Carbine model removing the rear iron sight to install a rail to mount the red dot stating the same logic.
He installed the RD direct to the rail. I’m considering mounting on a 1” raiser mount. Will not cowitness. Waiting for Fiber Optic 45° Offset Iron Sights (Flip Up) from usa optics.
Just moved the Red Dot forward to the chassis using the 1” raiser mount, then visually pre-zeroed the sight at 25 yrds centering/aligning the barrel aiming to the center of the 1” target, then using the lowest setting zeroed the RD.
Finally spent some time at the gun range. I felt very satisfied with the first 3 rounds zeroing the red dot at 25y. Adjustment was a different story as each red dot click was 0.5 MOA so I think I adjusted ok the vertical but the windage was a different story as I overdid it. At the end. I’m happy
I have a HOLOSUN AEMS circle/dot sight on my PC chassis carbine (and all the M*CARBO upgrades, natch), The only mount it came with was a bit too high. I waited foe a lower mount and it did come out recently - tooLOW!
So I bought MAGPUL 1/4" highsheek piece for my MAGPUL MOE stock that came with the RUGER PC. VOILE’ Perfectamundo! Now my eye aligns perfectly with tha AEMS and my MBUS co-witnessed sights. FAST and not expensive.
BTW, I mounted the AEMS on the BARREL Pic rail so it is always zeroed and it’s also easier to shoot with both eyes open when the sight is that far away.
If you have the OM stock and you feel comfortable with it then the lower you place your red dot the less sight angle you will have.
My suggestion is sight it in for 50yds if you can. That way you are good inside of that distance.
I do like Festus’s comment about mounting on the rail over the barrel.
This setup works fine for me.
I store this gun in a safe broken down (to save room for long guns). Every time I want to shoot It it goes back together. I have had no issue with going out of center.
I just mounted it on a QD so I can mount a scope when I desire.
The primary arms dot that is on this rig is 5yrs old. This one was made by Holosun and works real nice. Long lasting battery life. I run it at the lowest setting that I can see. Gives more accuracy and having it to the rear helps see it better and with the front end rested I think it gives more response of movement so adjustments can be made before the shot is made.
The new SLx sits a tad lower and works fine also, this is on 10/22 takedown
My sight intarget
Here’s my 9 mm PC with a HOLOSUN AEMS circle/dot sight on the barrel to maintain zero.
I have since added a 1/4" high MAGPUL cheek piece so now my eye aligns perfectly with both the AEMS sight and the MBUS “iron” sight. A fast and easy way to get proper alignment.