What Zero Distance for Your AR & Why?

[pntbllr228]

My Colt 6520 has an AimPoint H1 mounted on the carrying handle. The offset distance (sight line to bore line) is closer to four inches. POI is a solid three inches low at 25 yards.

Dan, what is the muzzle velocity used in your calculations? I assume its for a 55gr bullet, yes?

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I think he said he was using 75gr.

 

[dzelenka]

My Colt 6520 has an AimPoint H1 mounted on the carrying handle. The offset distance (sight line to bore line) is closer to four inches. POI is a solid three inches low at 25 yards.

Dan, what is the muzzle velocity used in your calculations? I assume its for a 55gr bullet, yes?

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I used a 75gr Hornady HPBT Match bullet at 2600. I get around 2800 out of that bullet in a 20" barrel. I knocked off 50fps per inch for the shorter barrel. The main reason I used that load is that is my SHTF ammo (I have enough for a nuclear winter).

Changing to a 4.0" sight height with a 200 yd zero would give you a -2.2" POI at 25 yds and a -0.8" at 50.

 

[RedhorseG20]

RUNNING whatever zero Remington put on my 870s bead. Waiting on pangris to get my 458 up and running and I bet the charts posted won't work for that.

The few classes Ive taken were taught by guys from the stone age that used 1970s techniques to fill a few graveyards.

 

[dzelenka]

Uh, no its not.

Ballistics Table in Yards
75 gr., .395 B.C. www.hornady.com
Range (yards) Muzzle 25 50 75 100 150 200
Velocity (fps) 2600 2544 2489 2435 2381 2276 2173
Energy (ft.-lb.) 1126 1078 1032 987 944 862 786
Trajectory (75 yd. zero)-2.5 -1.3 -0.5 0.0 0.1 -0.8 -3.4
Come Up in MOA -2.5 5.1 0.9 0.0 -0.1 0.5 1.6

 

[dzelenka]

Pangris, Ifn case that chart makes no sense, a 75 yard zero does not put your POI closer to the POA at the problematic 50 and under distances.

 

[tunatuk]

Anybody else find it funny that LSP972 and NolaCop always butt heads. Whatever works for the individual is what the individual should use. Old school, new school, or spray and pray. I don't care, as long as it gets the bad guys dead, the good guys alive, and no collateral damage.

Dead is dead, right? I doubt the guy that gets made that way will care if you are "running" an optic, or use 1970's, 1870's or 1770's tactics.

 

[dzelenka]

Anybody else find it funny that LSP972 and NolaCop always butt heads. Whatever works for the individual is what the individual should use. Old school, new school, or spray and pray. I don't care, as long as it gets the bad guys dead, the good guys alive, and no collateral damage.

Dead is dead, right? I doubt the guy that gets made that way will care if you are "running" an optic, or use 1970's, 1870's or 1770's tactics.

I don't know. 1770s tactics used a lot of bayonet work. That could be a long and unpleasant way of getting dead.

 

[nickatnite]

My AK is set to a 50 yd M.O.M zero. The M.O.M. being " middle of man". And as far as the 50 yd zero, well, that's about the distance from the front door to the edge of my driveway!

 

[Nolacopusmc]

My AK is set to a 50 yd M.O.M zero. The M.O.M. being " middle of man". And as far as the 50 yd zero, well, that's about the distance from the front door to the edge of my driveway!

That is a good point. Some consideration to what your "operating environment" will be should be taken when deciding what your zero should be. Granted, a threat can come in at any distance, but if you work in a urban and dense environment, your chances of making a 25 yard shot is much higher than making a 300 yard shot--your zero should reflect that.

Likewise, if you are in a genrally open rural area, with greater distance between buildings, house, etc, then maybve you want a rifle zeroed out a little farther.

Keeping in mind current LEO involved shooting statistics, a closer 50 yard zero may be more appropriate.

The only issue I see with a 25 yard zero, from a LEO, or even home defense situation, is that 25 yards is generally the maximum effective range of the average shooter with a handgun. Therefore, I see a 50 yard or 100 yard zero being more appropriate to be able to reach out when outside handgun distance.

Now, if the carbine is the primary or only weapon, then perhaps a closer zero is appropriate for home defense use given the closer contact distances.

 

[dzelenka]

Just looking at the numbers, an AR should not be zeroed for 25 yards unless you KNOW that you are shooting that close. A 25 yd zero puts the bullet almost 6" high at 100 yds and 9" high at 200. Whereas a 50 yd zero (or 200 yd for that matter) puts the bullet about 1" low at 25 yds, but not more than a couple inches high out to 200 yds.

 

[dzelenka]

So I am pretty smart after all?

Run your same XM193 numbers with a 50 yd zero and post them next to the 75 yd zero. I bet you find that the 25 yd number is in favor of the 50 yd zero.

 

[Nolacopusmc]

25 yard zero issues, written by tiger -

"There are some people using 25 yard zeroes, based on the fact that 25 yards and closer is where the majority of their shooting will take place, but this creates a couple of problems. First, even with a 25 yard zero, once you get 20 yards and closer you'll still have to compensate for the offset between the sights and barrel because the POI will be 2-2.5 inches lower than your POA. With body shots this may not be an issue, but for headshots, especially in a hostage situation, it is critical. The second problem with a 25 yard zero is that if you do need to take a shot from extended distances your POI will be way off. For example a shot from 100 yards with a 25 yard zero will have a POI around 6 inches high, again depending on weapon variables. Having to compensate for this much difference between POA and POI can be difficult, especially under stress."

As far as 50 vs 75 -

The chart I used before was actually based around a 150 yard max range -

For a XM193 out of a 16" -

0 -2.5
25 -1.42
50 -.58
75 0
100 +.03
125 +.31
150 -.01

So it is basically a 75/150 zero with less than an inch of variation from 50-150. At 150, XM193 MIGHT fragment, at 200, probably not going to happen. Six of one...

For the 75 SMK - a 50 zero looks a little better out to 150.

A useful tool -

http://www.handloads.org/calc/index.html

Just looking at the numbers, an AR should not be zeroed for 25 yards unless you KNOW that you are shooting that close. A 25 yd zero puts the bullet almost 6" high at 100 yds and 9" high at 200. Whereas a 50 yd zero (or 200 yd for that matter) puts the bullet about 1" low at 25 yds, but not more than a couple inches high out to 200 yds.

All of that makes perfect sense. I was generally referring to a rifle used solely for interior home defense. However, Height over bore will always be an issue.

Good gouge.

 

[dzelenka]

For interior home defense, the AR platform may not be the best thing. You might be better served by something with lower sights over bore. I was playing with an 8 X 57 JR double rifle the other day. It pointed real nice. Probably do an A NO.1 JOB at those distances. In all seriousness, The AR's inline stock is great for controlability and for less fine work at close distance than shooting a bad guy holding your wife in a way that shields most of his head. For that type of work, something with a lower comb and lower sight to bore distance would be better. The flip side is that lowering the sights makes hits at distance a bit harder (figure that one out ). No one gun is perfect for all applications. They are kind of like golf clubs.

 

[topgunz1]

50yds for me and every other AR the office has in service.

 

[joshuades]

I haven't read through all the way through the thread, just your opening post, so someone may have the same method.
I have my AR set up for hunting and it's devoid of iron sights, but I have my scope zeroed at 100yds. What I do is set the scope up to shoot about 2 inches high at 100yds (by way of elevation dial, which is zeroed at 100) to have a PBR of about 250yds with a 5 inch hit zone (MV of 2700fps). Because of the way the sights are set up on an AR (bore center to scope center on mine is 2.5", YMMV), it starts 2.5"low at the muzzle, apex at 2.5" high about 150yds, crosses line of sight at about 200yds, and drops below 2.5" low around 250yds.

 

[Nolacopusmc]

For interior home defense, the AR platform may not be the best thing. You might be better served by something with lower sights over bore. I was playing with an 8 X 57 JR double rifle the other day. It pointed real nice. Probably do an A NO.1 JOB at those distances. In all seriousness, The AR's inline stock is great for controlability and for less fine work at close distance than shooting a bad guy holding your wife in a way that shields most of his head. For that type of work, something with a lower comb and lower sight to bore distance would be better. The flip side is that lowering the sights makes hits at distance a bit harder (figure that one out ). No one gun is perfect for all applications. They are kind of like golf clubs.

Agreed. Rifle is generally not best choice for HD, but for those that insist, closer bzo may be better option.

I also agree with Pangris that it us more an art depending on rifle, ammo, max range, and adversary.

 

[Paul Gomez]

I don't know. 1770s tactics used a lot of bayonet work. That could be a long and unpleasant way of getting dead.

Yeah, but the guns were a lot longer and they didn't break into two pieces when you smacked somebody really hard.

 

[Paul Gomez]

The computer just ate my elegant and witty response, so ya'll are stuck with this one.

Actual 25M zeros suck. If you are aiming at 25M and printing 'an inch & a quarter low', that's not a 25M zero. If you are adjusting your sights to 8/3 [or 6/3] and coming forward 1 click, that's not a 25M zero.

You cannot adjust iron sights or optics to give POA/POI inside the dreaded 25M. The only way to address line of sight/line of bore issues inside 25M is to physically shift your POA to allow for desired POI. Some people consider this to be an issue. Some do not.

Even if your expected ranges never exceed 25M, there is nothing lost by getting a more useful zero, be it 50/75/100 or 200. If your shooting ever does go beyond 25M, there are huge negatives to a strict 25 zero.

One of the biggest issues with the AR platform is line of sight/line of bore. Iron sights generally sit 2.5 inches above the center of the barrel. Depending on optic design, mount design and mount position, these numbers only increase. Every increase in LOS/LOB increases offset differences at any given range.

 

[SKYWLKR]

I sight in for 1" under at 25 and may need to move it a hair to make sure it's an X at 200.

So I guess I have a 200 yard Zero...

 

[Nolacopusmc]

Actually, I'd say the .223 is an ideal home defense round with proper ammo selection. Done right it overpenetrates less than handguns and has far better terminal performance. There are other considerations but given the option between an AR, handgun of any caliber, or shotgun with any load - in my house - AR every time.

trudth