I guess I can zero my RDS on my workbench

[BarboursvilleBill]

I bought another AR that has the traditional A-2 front post and a flip-up BUIS on the rear. I am installing one of my old TRS-25s on the rail, and am using a UTG medium height QD 3-slot mount for it, which means it will be absolute co-witness. My irons are already zeroed, so I'm guessing all I will need to do is simply point the red dot at the front post while in the cradle on my bench.

What I'm asking is: 1) there seems to be no way to separately zero the RDS and the irons, correct? and 2) I can run around shooting with my rear flipper down and just look at the red dot, right? (That's what I do with my other AR that does the 1/3 drill.)

BTW, I chose absolute because of the cheek weld on my new piece.

 

[Varminterror]

For absolute, yes, in theory, you can look through your sights, and set the dot in line with the post - but only when viewing the post through the rear sight.

For absolute, when both are zeroed at the same range, then there's no other position the red dot will land when zeroed - except right in the way. Yes, you can "run around shooting with your rear flipper down..."

 

[Chuck R.]

You can use 2 zeros IE:

Irons at 25m
RDS at 50M

But you will lose the ability to co-witness, meaning you can't have your irons zero'd and adjust your RDS dot to sit on the post while looking through your rear aperture. IF you do move the dot back onto the post, you'll basically have both with the same zero. I use a lower 1/3rd co-witness and it works the same as an absolute except the sights and dot line up in the lower 3rd of the RDS tube.

BTW, when ever I've co-witnessed and RDS with irons (regardless of absolute or lower 1/3) it was "close", but not perfect. As the distances increased, the error becomes more apparent. The co-witness is good for CQB distances and to check to see IF something got whacked out of alignment, but I've always gone ahead and zero'd the RDS when I had time.

Chuck

 

[imashooter]

There's a whole bunch of data regarding a red dot "lollipopping" atop the front sight or even aligning for that matter. Only one of mine has aligned and luckily, it also sat right on top of the front sight (lollipop). If your plan is to use your hard sights without removing the red dot, I would zero the red dot at distance X. I would zero the hard sights, viewing through the red dot optic, at whatever distance you prefer. I'd zero through the optic to factor in any distortion regardless of reason for distortion. It's very common at distances beyond "in yo face" for the dot to be noticeably offset from the hard sights. I find it to be the rule and not the exception. Just treat each as though the other isn't installed.

 

[BarboursvilleBill]

Thanks a lot, everybody!

I didn't think I could get very excited about having another 'AR platform' rifle, but I'm very happy with it. (FYI, it's a new Savage MSR-15 Patrol that's supposed to have a really great barrel in it, according to the gun writers.) I just received the UTG medium QD mount, and stopped everything I was doing to put it on. I think it's going to be a challenge to learn how to look for the red dot and see the post underneath it.

When I purchased my new piece (a backup to my Colt M4 that has a 1/3 co-witness Vortex SPARC AR) I sprung for a Bushnell AR/223 scope and a QD mount, thinking that if the barrel is so good, perhaps it's worth putting some magnification on it. But later I decided to put my old TRS-25 on it and have the ability to swap them out depending upon the conditions.

The carbine with an empty mag and sling weighs just 7lbs, and with the red dot will add only about another six ounces. This piece with the scope on it weighs about 8lbs 5oz. Huge difference, unless one has a bench or set of shooting sticks to launch it from.

My results at the range at 100yds, using the AR/223 scope on 3 1/2 power, were not any better than what I experienced with the red dot on the Colt--about a 2 inch group. So why carry all that weight? I know, distance: but the cartridge runs out of gas at about 350yds according to the ballistics chart--400lbs/ft.

 

[BarboursvilleBill]

CONCLUSION: At the range yesterday, zeroing the "absolute" red dot was easier than I thought it would be. I learned that I don’t have to crank the red dot down on to of the front post, although I started there. All I had to do was simply flip down the rear sight and zero in the dot. from then on, where the dot appears depended only upon my cheek weld; sometimes it was over or even next to the front sight--the POI was always wherever the red dot was. Because this was not a 1/3 co-witness as on my Colt, I had confused myself.