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Old April 3, 2018, 05:24 PM   #1
kymasabe
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New To AR platform: rear sights? Sighting in? Same plane apertures? Bullet arc vs bullet weight?

OK, lots of questions. I've had plenty of rifles in the past, but new to the AR. I built two in the past but sold them before I had a chance to sight them in. A decade of AK's and 123/124gr ammo hasn't prepared me for AR sights and varying bullet weights. So...here goes.

1. I'm looking for a fixed rear sight for my AR, I don't plan on using an optic, I'm a big fan of keeping it simple. Have narrowed my selection to Daniel Defense OR Troy Di-Optic. Was leaning towards the Daniel Defense until this morning when I read that the Daniel was dual plane apertures and the Troy is single plane aperture. Honestly, I'll probably never shoot past 200 yards with it so...do I really need dual plane?
2. Which leads into the next question. Sighting in. My understanding is that the bullet travels in an arc, passing that same plane twice, once as it rises and once as it falls. What are those points? 25 and 100 yard? 50 and 200 yards?
3 Which leads me to my third question: Bullet weights. Once I get the rifle sighted in with 55gr .223, will there be a big difference with 55gr 5.56? And If I want to go hog hunting and move up to a 75gr BTHP, will I need to totally resight the thing, or will I still be fairly close? (1:7 twist, range 50-100 yards for hogs).
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Old April 3, 2018, 05:37 PM   #2
Nathan
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1) Basically, dual plane aperatures are std. they allow you to be more accurate up close when the small aperature is sighted to a 300 zero point.

2) For XM193 55 gr and a 16” tube, 50:200 works out close. You need and app like JBM Ballistics to figure out.

3) meh....what’s big? Yes, it will be different, it will depend on loads selected and how the barrel reacts to changing loads.

If you are shooting irons, you are giving up speed and accuracy for balance and weight...frankly, I would get a decent reds.
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Old April 3, 2018, 05:52 PM   #3
Bartholomew Roberts
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1. The nice thing about a same-plane aperture is you can switch to the small aperture at distances under 300m without shifting your zero. If you aren't going to shoot past 200, I don't see much advantage to a dual plane aperture.

2. Very roughly speaking - 25yds/300yds and 50yds/200yds

3. .223 is very flat shooting in almost all bullet weights. At 50-100yds, you won't be missing any hog vitals due to shifts in point of impact caused by different ammo.
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Old April 3, 2018, 06:01 PM   #4
raimius
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Yes, ballistic trajectory usually crosses the sight's "zero" line twice. (Very rarely just once, but it is possible). Where the "zero" intersects depends on how you zero the rifle. The most common (1st) zero distances for AR-15s in .223/5.56 are 25, 50, and 100 yds. Personally, I like the 50yd zero because it keeps the bullet within about 4in of point of aim between 0yds and 300yds with 55gn fmj. Other zero distances have flatter initial arcs or longer arcs within some user "acceptable" difference.

https://www.ammoland.com/2014/06/how...#axzz5BeVs0pIM
https://robarguns.com/blog/2013/11/2...-has-it-right/
For some more detailed reading...
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Old April 3, 2018, 07:21 PM   #5
marine6680
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A single plane sight is best for inside a few hundred yards. I run the small appeture most of the time. The large appeture is for speed at close range, not necessary precision. I don't want a shift in zero due to using a different appeture.

One of the most useful zeros for an AR, using 55gr 5.56 spec ammo is the 50m zero it's initial zero is 50m and the far zero is 200m.

Many people just zero at 50yds, and call it 50/200 but it's more 50/225 in yards.

It's useful because between 0-250 yards, the bullet is no more than 2in high or low from the point of aim. And only a few more inches low at 300yds.


There will be a difference between 223 and 556, and with different weight bullets, but inside 100yds, not enough to matter for most uses.

There is an app for smartphones, Strelok... It is a very good ballistics calculator. The free version can do the calculations most need, with extra features and additions for the paid versions.


For hunting hogs and home defense, if you ever go that route... I suggest a good red dot sight. Speed and ease of use go up drastically over irons. Especially past 25yds. Then a simple back up sight like the MBUS is perfectly fine to go along with it.
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Old April 3, 2018, 07:37 PM   #6
Mobuck
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"3 Which leads me to my third question: Bullet weights. Once I get the rifle sighted in with 55gr .223, will there be a big difference with 55gr 5.56? And If I want to go hog hunting and move up to a 75gr BTHP, will I need to totally resight the thing, or will I still be fairly close? (1:7 twist, range 50-100 yards for hogs)."

Really?? What is it with the .223/5.56 thing lately? Look at the ballistics charts and you'll see there's little difference in velocity between .223 and 5.56 with a 55 grain bullet. Changing the bullet weight by 37%(75 vs 55) will most likely change the POI even with no optic. Failing to recheck that POI before hunting is unethical.
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Old April 3, 2018, 08:34 PM   #7
imashooter
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Teach yourself to use a ballistics calculator. There are several freebies to use online. Here's the one I used in the past. The graph isn't great (appearance wise) but it is usable. The chart is very readable. I would copy the chart and paste into Word, etc. Save the graph as an image, perhaps sharpen it a bit then finally insert into the document containing the chart. Works well. http://www.shooterscalculator.com/ba...tory-chart.php
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