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post #1 of 15 (permalink) Old 11-15-2011, 01:19 PM Thread Starter
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sighting in a red dot

I have a Bushnell TRS-25 red dot sight. it is zero magnafacation it's a 2 MOA dot. I'm putting it on my AR. I was told to zero it in at 25 yards and it should be good out to 100. Should this work?

I Zeroed it in at 100 already and went to shoot a 3 gun match over the weekend and could not hit any of the 3 inch steel plates set out at 25 yards. My friend let me use his AR with a red dot and it shot perfect. he's the one that told me to sight it in at 25 and it would be good out to 100.

Just checking before I go out this weekend and sight it in on what others do. Thanks for any help.
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post #2 of 15 (permalink) Old 11-15-2011, 01:41 PM
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Re: sighting in a red dot

About 1 1/2 inches high at 25 should put you on at 100.




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post #3 of 15 (permalink) Old 11-15-2011, 03:08 PM
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Re: sighting in a red dot

Quote:
Originally Posted by John S
About 1 1/2 inches high at 25 should put you on at 100.
This depends on several factors, the most critical being the ammo and sight height. I suspect, though, that an AR15 sighted 1.5" high at 25 yds is going to hit way high at 100 yds.
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post #4 of 15 (permalink) Old 11-15-2011, 03:15 PM
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Re: sighting in a red dot

FWIW, most centerfire rifles will hit slightly low (.5" to 1") at 25 yds when zeroed for 100 yds. This is assuming a 1.5" sight height (center of bore to center of scope). I believe ARs usually have a greater sight height (~2.5" ?). This means that the bullet will impact even lower at 25 yds when zeroed at 100 yds... approx. 1.5" low according to my ballistics calculator.

I would imagine that you were shooting right under the 3" targets at 25 yds when you aimed for the center. The best thing to do is go shoot some paper before you make any adjustments.
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post #5 of 15 (permalink) Old 11-15-2011, 07:09 PM
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Re: sighting in a red dot

ARs in 5.56 benefit from sighting in at 50 yards... which will put you pretty much dead on at 200 yards as well. Thus zeroed, your POI will be no more than 2 inches above or below POA out to about 250 yards. Small variations on these numbers will occur due to bullet weight and barrel length.

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post #6 of 15 (permalink) Old 11-16-2011, 05:25 AM
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Re: sighting in a red dot

I use the target from the eotech site. It is downloadable in pdf form.
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post #7 of 15 (permalink) Old 11-16-2011, 11:13 AM
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Re: sighting in a red dot

A zero at 25 yards should put you roughtly zeroed around 250 yards.

You should actually be -1.5" at 25 yards to get a 100 yard zero. You need to remember than the iron sights on an AR rifle are about +2.5" above the bore. If you co-witnessed your red dot, then it will be the same height.

Using the Point Blank Ballistic Program and using the following info; 55gr bullet @ 3240fps with a +2.5" sight height it tells me the following;

25yds : -1.5"
50yds : -0.78"
75yds : -0.27"
100yds: 0.00"

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post #8 of 15 (permalink) Old 11-17-2011, 04:47 PM
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Re: sighting in a red dot

Quote:
Originally Posted by Steve in PA
A zero at 25 yards should put you roughtly zeroed around 250 yards.

You should actually be -1.5" at 25 yards to get a 100 yard zero. You need to remember than the iron sights on an AR rifle are about +2.5" above the bore. If you co-witnessed your red dot, then it will be the same height.
Steve knows what he is talking about!

are you shooting a 16" or 20" AR platform?

Are you in search of a battle sight zero? i.e. 25 meter zero that will enable you to hit center mass on 20" wide silhouette out to 300m with out making adjustments?
if so here is a target http://ohmr.ohio.gov/forms/ohmr2444-b.pdf

Are you looking to drive tacks at 100yds???
if so then bench rest at 100 and put a 2" circle on the target. Your 2 MOA red dot will easily put all rounds into that circle.

SGT CARL J. MORGAIN KIA IRAQ 22 MAY 05
A CO 1/112 INF TF 2-7 US ARMY
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post #9 of 15 (permalink) Old 11-17-2011, 05:02 PM Thread Starter
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Re: sighting in a red dot

I have a 16 inch AR. I'm just looking to shoot 3 gun matches. And need it to shoot close up say 25 yards and out to 100 yards.
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post #10 of 15 (permalink) Old 11-17-2011, 06:59 PM
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Re: sighting in a red dot

Well, if you are planning on running a 100 yard zero then you need to realize that you will be shooting -1.5" at 25 yards. There is no way around it.

Steve
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