In the past with red dots on ARs I've always gone for absolute cowitness with iron sights. I really don't have any compelling reason for it other than I kinda like the dot aligning smack dab in the middle of the sight picture. Comforting kind of thing I suppose, since that's how reticles tend to get you to fixate where the POA is in magnified scopes and such.

But now I'm setting up a RMR on a lightweight 5.56 mid-length build and I've been mulling over using an ADM QD mount this time. I've had good results using their mounts with T1s in the past so I figure the same would be had with the Trijicon. But the thing is, the mount for absolute co-witness is frickin' HUGE (looking), kinda visually (and physically) contrary to the point of making the gun as light as possible.

EDIT:
So now I'm thinkin' (always a dodgy thing, that thinkin' stuff) that I should go with their 1/3 co-witness mount instead. It's visually has a lot less mass to it, and certainly is a bit lighter and thus is in keeping with a "lightweight build". I think I can adapt to a 1/3 setup, but it'll be my only RDS rifle that's configured this way.

I've been thinking again, again dodgy...lower 1/3 co-witness should have a taller mount, right? Even MORE height/mass. Never mind...

So what does the gallery think? Am I overthinking this? Is it not a big deal? Or should a person just man up, say to hell with trying to scrap away a few ounces, and live with the bigger mount because it's more important to maintain consistency across rifles with what's been so far tried, trained for and true? What are others' preferences between the two co-witnessing planes?

This message has been edited. Last edited by: soggy_spinout,

I prefer absolute co-witness because I like everything to line up so if I were using my Aimpoint and it crapped out I wouldn't have to adjust my cheekweld for the lower irons.

For RMR mount have you looked at Scalarworks? I have no first hand experience but see people recommend them for lightweight builds often.
https://scalarworks.com/shop/optic-mounts/ldm-rmr/

I prefer absolute, it gives a greater field of view.

My personal rifle is absolute, my duty rifle is 1/3.

Both can be made to work.

SR025,

Actually something has been bugging me since posting the OP...lower 1/3 co-witness should result in an even TALLER mount, not shorter. I have it backwards. Or at least FUBAR'd. I was reading the description of the short QD mount on some website and whoever wrote that passage said "1/3 co-witness" and I being the tired schlep that I am, accepted it without question. Non-firing brain cells will get me every time.

It appears that the short ADM mount does no kind of co-witnessing with AR sights. It's just a short mount. Suitable for other kinds of guns, I suppose. Their SOCOM height QD mount obtains lower 1/3 co-witness, and yeah it's even 'huger'.

Thanks for replying. With ADM I have my answer. But to your observation: I'm not sure why the cheek weld would be different. 1/3 or absolute, you're still going to be aligning with your sights regardless, so it should be the same cheek weld every time.

The Scalarworks mount is interesting. And is it light; 2 oz. less than the ADM absolute co-witness QD. More expensive...over double the cost in fact, but when is shaving weight ever cheaper?

quote:

Originally posted by tanksoldier:
I prefer absolute, it gives a greater field of view.

My personal rifle is absolute, my duty rifle is 1/3.

Both can be made to work.

Thanks, that's what I sort of figured. Shoot anything enough and us humans will adjust.

quote:

Originally posted by soggy_spinout:
What are others' preferences between the two co-witnessing planes?

We had a recent thread on that topic: https://sigforum.com/eve/forums...0601935/m/4540075524

Depends on your cheek weld. I shoot squared up to the target with my head pretty upright. Lower 1/3 lines the dot up better for me, I have to drop my head a bit to get on the irons. Irons cheek-weld is perfect in the prone, but that's not how I'd be fighting.

With the few rifles I've played with, absolute seemed more natural to me.

Absolute, especially with flip up BUIS. Once you sight in with one sight, you can use that to adjust the other to match.

quote:

Originally posted by Dwill104:
Absolute, especially with flip up BUIS. Once you sight in with one sight, you can use that to adjust the other to match.

You can do that with either absolute or lower 1/3d. So long as you can see the irons through the optic, you can adjust the dot to the irons (or vice-versa).

This is only a rough method of zeroing though, still need to fine tune the zero of whichever sights you adjusted to the other on the range.

Last time I zero'd my M4 irons, then moved the dot to the irons, I was hitting the top left corner of the 81/2" x 11" zero target at 25m. So, still a lot of adjustment needed to get the dot zeroed.