AR-15 trajectory/zeroing?'s [Archive] - Glock Talk

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farmer2
01-01-2011, 16:37
When sighting in my new BCM mid-length I found that my new magpul rear sight had a different zero based on the aperture I was using. The large aperture hit 2.5-3 inches lower at 25 yrds. At first I thought something was wrong, but upon researching the topic I found that the 0-2 sight (big opening) will be zeroed at 200meters while the unmarked aperture will be zeroed at 300meters. My targets at 25 yards tend to line-up with this train of thought. However, I'm not sure this makes a lot of sense to me. For example, I plan on using my carbine for home defense and it makes sense to use the "large" aperture because of the increased visibility and more rapid target acquisition. However, at home defense ranges this will put me shooting a couple inches low, which is not good if any precision is required. It seems to me that this would be a problem in a military combat environment as well. I am relatively new to AR-15 open sights (all my previous AR-15 experience was with a scope), so it is more than possible that I am missing something. Please set me straight on my thought process and/or let me in on how you deal with this issue. Thank you very much!


farmer

faawrenchbndr
01-01-2011, 16:42
I use a 36m zero

http://www.biggerhammer.net/manuals/mcrp3-1a/3-01-1/ch6c.pdf

NeverMore1701
01-01-2011, 16:43
I use the large aperture, and zero at 50 yards. That will keep you within a couple of inches of your point of aim from 50 yards to 200 meters. Best all around zero from what I've seen.

farmer2
01-01-2011, 16:53
I use a 36m zero

http://www.biggerhammer.net/manuals/mcrp3-1a/3-01-1/ch6c.pdf

But won't your large aperture still be low by 2-3"s at the 36m zero?

farmer2
01-01-2011, 16:57
I use the large aperture, and zero at 50 yards. That will keep you within a couple of inches of your point of aim from 50 yards to 200 meters. Best all around zero from what I've seen.

This might be my best bet. So, you don't use your long range aperture at all? Because a 50m zero with your large aperture would put your small aperture way high at most long range distances....correct?

farmer2

cowboy1964
01-01-2011, 18:22
An AR has about a 2.5-2.7" inch sight offset. You're not going to get ultra-precision shots at varying close ranges. Get a laser bore sight for $40 and do some experimentation. It's an eye opener.

Get an EoTech. As long as the 65 MOA ring is on your target, you'll hit it.

DougW
01-01-2011, 19:07
Large ap at 50 yards. Scopes zeroed 2" high at 100 yards. Covers out to 300 yards for me.

farmer2
01-01-2011, 20:03
Large ap at 50 yards. Scopes zeroed 2" high at 100 yards. Covers out to 300 yards for me.

what scope are you using?

Infallible
01-02-2011, 11:50
I use the large aperture, and zero at 50 yards. That will keep you within a couple of inches of your point of aim from 50 yards to 200 meters. Best all around zero from what I've seen.

this is the most common unless you are shooting long distances.

mjkeat
01-02-2011, 11:58
I was under the impression the large aperture was for low light and small for normal light conditions. Thats what we were taught anyway.

scromer
01-02-2011, 13:24
http://www.m4carbine.net/showthread.php?t=65679

This may help.

DougW
01-02-2011, 15:11
farmer2, I use a Leatherwood 1.5X6 on my "match" AR. Targets at 3 gun matches can be out past 300 sometimes.

Using open sights, I have always used the large ap all the way to 200, then the small at 300 (if I can see that far!). (I have a 20" A2 and a 16" XM177E4??? that are both set up with open sights zeroed at 50 yards that pits me on at 200 too.) Other rifles have the Leatherwood, a TA31F ACOG, and an Aimpoint ML2. The ACOG is zeroed at 100 yards, then then I use the bullet drop marks out to 600 yards (tough shooting past 300 with a 4 power and my old eyes).

farmer2
01-02-2011, 21:48
http://www.m4carbine.net/showthread.php?t=65679

This may help.


This is the thread that lead to my frustration. If you sight in your rifle based on the 300 yard zero (small aperture) your large aperture will be 3 + inches low at 25 yards, which for me (home defense) is not precise enough. If i sight in at 25 yards with my large aperture, my small aperture will shoot extremely high at long range distances. I wish both apertures had the same zero, that would solve my problem. Does anyone make such a sight?

farmer2
01-02-2011, 21:49
I was under the impression the large aperture was for low light and small for normal light conditions. Thats what we were taught anyway.

this is is true, but both sights do not have the same zero, so it is more complicated than that.

faawrenchbndr
01-03-2011, 04:10
What rear sight are you using?
If you have a folding rear sight, you can get a "same plane" rear sight.
This will eliminate your concern

scromer
01-03-2011, 05:34
Or you can get an XS Same Plane aperture for you A2 or A1 style sights.

I sight in the small aperture at 50 yards which handles 95% of my shooting.

farmer2
01-03-2011, 07:16
What rear sight are you using?
If you have a folding rear sight, you can get a "same plane" rear sight.
This will eliminate your concern



This is exactly what I need, any recommendations? Currently I am using a magpul rear sight.

thank you

scromer
01-03-2011, 08:47
http://www.aimsurplus.com/product.aspx?item=XTSSIGFBSROBT&name=Troy+Ind.+Rear+Folding+Battle+Sight+Black&groupid=48

Same plane and arguably the best folding sight on the market.

BBJones
01-03-2011, 14:31
I think I understand your question. The sights are higher than your barrel by 2.5" approximately (look up "height over bore"). If your sights were zeroed at say 7 yards for home defense, they would only be zeroed at precisely 7 yards ( I know there would be a second zero but not important for this discussion). At 0 yards your POI (point of impact) would still be = height over bore. at 15 yards your POI will be significantly higher than POA (point of aim).

The better solution is to pick your zero (say 50/200) and practice inside 50 yards knowing that you are dealing with a height over bore issue (ie aim higher than what your sights indicate).

faawrenchbndr
01-03-2011, 17:26
This is exactly what I need, any recommendations? Currently I am using a magpul rear sight.

thank you

Troy makes a "same plane" rear sight as well as ARMS

farmer2
01-03-2011, 20:19
I think I understand your question. The sights are higher than your barrel by 2.5" approximately (look up "height over bore"). If your sights were zeroed at say 7 yards for home defense, they would only be zeroed at precisely 7 yards ( I know there would be a second zero but not important for this discussion). At 0 yards your POI (point of impact) would still be = height over bore. at 15 yards your POI will be significantly higher than POA (point of aim).

The better solution is to pick your zero (say 50/200) and practice inside 50 yards knowing that you are dealing with a height over bore issue (ie aim higher than what your sights indicate).


BBJones, thank you for your response, but I don't think my post came through clear (most likely my poor language skills). I do understand the sights are above the axis of the bore, but that is not my problem. My problem is that the two apertures on a standard ar-15 sight have different zeroes by as much as 5 inches and worse at longer ranges.


faawrenchbndr, thank you for the recommendations.

faawrenchbndr
01-04-2011, 05:03
Anytime,.....hope we all were helpful

Sure wish I was in Spokane! F-i-L is in Kettle Falls, about 90 miles NE of you.

farmer2
01-04-2011, 06:47
http://www.aimsurplus.com/product.aspx?item=XTSSIGFBSROBT&name=Troy+Ind.+Rear+Folding+Battle+Sight+Black&groupid=48

Same plane and arguably the best folding sight on the market.

thank you

farmer2
01-04-2011, 06:49
Anytime,.....hope we all were helpful

Sure wish I was in Spokane! F-i-L is in Kettle Falls, about 90 miles NE of you.

at the risk of sounding incredibly naive, what is F-i-L?

faawrenchbndr
01-04-2011, 08:32
at the risk of sounding incredibly naive, what is F-i-L?

Father
in
Law

Novocaine
01-04-2011, 11:34
Magpuls are not the same plane? Interesting, I thought itís almost expected from the BUIS to be the same plane.

Farmer, I wouldnít worry about the rifle hitting couple of inches low at 25 yards. First of all two inches are more than accurate.

Secondly itís pretty much impossible to get AR hit precisely to the point of aim at close distances anyway. If your sights are zeroed at 25, your POI will shift south pretty radically at closer distances and north at longer distance. If your AR hits couple of inches low at 25 the POI shift will be very gradual all the way to the contact distance.

So even the same plane BUIS should hit low at 25 when properly regulated.

Halojumper
01-04-2011, 12:53
I was under the impression the large aperture was for low light and small for normal light conditions. Thats what we were taught anyway.

I don't know what the current doctrine is, but way back when we were taught that the large aperture's main purpose was long distance shooting and the small one was for closer. And, we were also told (as were you) to use the "long range" aperture for low light conditions. If this is still true, then the large/low light aperture should be a little taller or longer than the other one. It should be an easy matter to measure it. In fact, I'll go out to the safe and take a look later.

NeverMore1701
01-04-2011, 14:13
I don't know what the current doctrine is, but way back when we were taught that the large aperture's main purpose was long distance shooting and the small one was for closer. And, we were also told (as were you) to use the "long range" aperture for low light conditions. If this is still true, then the large/low light aperture should be a little taller or longer than the other one. It should be an easy matter to measure it. In fact, I'll go out to the safe and take a look later.

I think it's the other way around. Large aperture is for 0-200m and low light, small aperture is for long range.

Halojumper
01-04-2011, 14:24
I think it's the other way around. Large aperture is for 0-200m and low light, small aperture is for long range.

Since it's been a while, I checked TM9-1005-319-10 and it looks like what I said was correct.

ETA: No, I take that back. You are correct. It does say to use the large aperture for "very close" range and night. The example they gave was rooms and jungles.