AR 9mm zero distance.

[Leon tP]

Is that center of the bore to center of the scope/sight? With a measuring tape and eyeball I'm about 2.5 inches from center to center.
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It's already been mentioned, first decide what range you want to shoot most frequently. You mentioned Maybe between 40 to 75 yards so how about 50 yards? Next decide on a load you like and want to load then chronograph it so you know how fast it's actually going from your AR. Finally, go to a website like JBM and use their ballistics calculator. I've noticed that RMR RN bullets are fairly similar to 124 grain Hornady fmj rn (BC 0.145). Knowing your sight offset height of ~ 2.5" and guessing a muzzle velocity around 1300 fps (you'll have to measure the actual speeds you get). I ran some numbers at JBM with a 50 yard zero and I got back about 1" inch low at 20 yards and about 4" low at 100 yards. So a 50 yard zero would be very flexible. It would be pretty close to point and shoot out to 100 yards.
In the end though, if you want more accurate details in trajectory predictions, you'll have to input actual bullet speeds from your own loads. I was just making a guesstimate base on the general info you've provided.
The last step, just get out there and shoot stuff, that'll determine how close all the calculations really are.
Hope this helps.

 

[Waterboy3313]

I got a chance to shoot my 9mm upper today. I ran 10 rounds through it total. The scope I had on it failed. I tried to adjust it and noticed the cross hair was broken.

Either way with a broken scope it was on paper and a decent group. Disappointed with scope issues but I am looking forward to trying it again.