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View Full Version : weird time trying to zero at 50 yds (AR15) input please...


jonjonkills101
04-19-2012, 3:08 PM
so long story short...when i first assembled my AR and proceeded to test fire and zero at 25 yards, I had zero trouble. a couple clicks of windage and i was dead on for 25 yards. best group when i took my time was about an inch or 2 dead center offhand. my normal grouping when i shoot faster is probably like 4-6 inches.

today i tried to zero at 50 yards. looking at trajectory charts i expected to have to make at least some elevation adjustments. but when i started off first (bench w/ bipod) i was already dead center. thinking it was because my cheek weld and aiming changed since i switched from off-hand to bench i decided to try shooting offhand how i usually shot at 25 yards. my group was again dead center where i was aiming and maybe opened up an inch or 2 in diameter since it was further. (i made zero adjustments)

this is with an adams arms midlength 16" with LMT fixed front sight and detachable carry handle sight. ammo was 885 and 193.

does this seem right? i understand i changed some variables by shooting bipod off the bench. and i'll be honest, i had a tough time since this is my first evil rifle and first time shooting with irons. i just didn't expect this kind of outcome.

Dark Mod
04-19-2012, 3:10 PM
Isnt a 25 yard zero supposed to be good to about 250 yards? im sure there is a little bit of difference but it should be pretty small i would think

jonjonkills101
04-19-2012, 4:06 PM
maybe i was overthinking it since i read a lot into it. there was a good write up on m4carbine.net. i didn't actually chrono my rifle but the write up had trajectories for the same ammo i was using with a 16 inch barrel, so i figured it would at least be a good reference.

according to that, my 25 yard zero should hit about 2-3 inches high which was what i was expecting to happen, but it did not...just hit center as if it was already zeroed for 50.

mif_slim
04-19-2012, 4:34 PM
Check if your front end is its tight and not loose. Barrel flex (which I havent heard of yet in the AR platform) might have changed the POI. I know this happens on SU-16's. When mounted on Bi-pod (stock or after market) it changes the POI because the reciever is polymer and flexes.

G60
04-19-2012, 4:40 PM
Looked at the wrong chart.

jonjonkills101
04-19-2012, 4:42 PM
Check if your front end is its tight and not loose. Barrel flex (which I havent heard of yet in the AR platform) might have changed the POI. I know this happens on SU-16's. When mounted on Bi-pod (stock or after market) it changes the POI because the reciever is polymer and flexes.

i checked to make sure the sights were all tight before i began shooting. (which i do before shooting every time) i suspected the bipod might have played into it like that somehow, or at least changed my cheekweld position and how i aimed that way. but i also did remove the bipod and try shooting offhand how i usually shoot offhand comfortably and had the same result just less accurate.

some other facts are, after every range trip i clean my rifle pretty well and freshly oiled, i did nothing to change that. also my rifle only has shot 855 and 193 at both 25 and 50 so it shouldn't be about the ammo.


POI for most .223 loads will only change about a half-inch from 25-50 meters.

you know what, for now...i'll just call today a success, and blame myself for overthinking a simple task. i mean if anything i was hitting where i was aiming for at 50 yards. as long as i aim how i usually do, i should be ok. this rifle will never see an optic, i just want to get better at aiming with iron sights. if i want to be more precise, then i'll take out the 700. i'll probably try out shooting the AR at 100+ yds next and see how the POI behaves.

killshot44
04-19-2012, 4:55 PM
If you zero'd at 25yds and shot at 50 your POI should have been 1.75" lower. That's a small enough amount to disappear into the wobble-zone when shooting offhand unless you're experienced.

Unless you must have a "battle zero", I'd zero the thing in at the distance you're going to shoot the most often using a bench and sandbags. Then learn your holds for different distances.

duggan
04-19-2012, 5:02 PM
It's because the AR platform is soooo awesome you don't even have to aim IT KNOWS WHAT YOU WANT TO HIT. Next time you go to the range point it at a target but close your eyes and think about/visualize the round hitting a different target and thats where the round will go:cool:.

HighLander51
04-19-2012, 5:04 PM
Rifle trajectory is parabolic, so a 35 yard zero will zero again at 350 yards, less than 35 and greater than 350 it will shoot low, and between 35 and 350 it will shoot high. a 50 yard zero will put your 25 yard shot 1.4" low. For an iron sighted AR, you typically want a 200 yard zero, which is 1.7" low at 25 yards, 1" high at 100, and 2.7" low at 250 yards. That gives you a 4" window from 0 to 250.

There are a number of ballistic programs online that can graph the trajectory. You need to specify bullet weight and sight over bore height. Most programs do not adjust for barrel length, however muzzle velocities are provided so you can estimate the difference between a 20" and 16" barrel. And remember you will be 'half clicked' at the far zero, ie, for 68/200 yard zero, you may hold a 1" group at 68 yards, but a couple of clicks will throw it 12" at 200. You get close at 68, then check at 200, it may be that you can only get 2" high and right because of the number of clicks. Always go high and right for a right hand shooter, and at 68 yards, you will not even see it.

G60
04-19-2012, 5:15 PM
you know what, for now...

Ignore my math, I was calculating with sights 1.5" over bore...not 2.5 like I should have.

killshot44
04-19-2012, 5:21 PM
Ignore my math, I was calculating with sights 1.5" over bore...not 2.5 like I should have.

1.5" SOB(sight over bore) gives a drop of 1.25" from a 25yd zero to 50yds. a 2.5" SOB changes the drop by 1", so that is 2.26" at 50yds.

My earlier thought remains.

WETP
04-19-2012, 5:21 PM
jonjonKills101,

Good for you for realizing that something was wrong. But after ready some the comments, please remember that is one of your more important responsibilities to know your holds and where your hits will end up. I recommend that you choose your zero distance and the check at as many as your range allow you. Base on my zero at 25yd my 50yd will be around 3" high and 75yd + 1-1.5" higher than 50yd. with Federal XM193 55gr.

That's just me. don't believe or use my numbers. Go out a get yours.

Have a good shooting!!!

jonjonkills101
04-19-2012, 5:31 PM
It's because the AR platform is soooo awesome you don't even have to aim IT KNOWS WHAT YOU WANT TO HIT. Next time you go to the range point it at a target but close your eyes and think about/visualize the round hitting a different target and thats where the round will go:cool:.

exactly why i have an AR haha

jonjonKills101,

Good for you for realizing that something was wrong. But after ready some the comments, please remember that is one of your more important responsibilities to know your holds and where your hits will end up. I recommend that you choose your zero distance and the check at as many as your range allow you. Base on my zero at 25yd my 50yd will be around 3" high and 75yd + 1-1.5" higher than 50yd. with Federal XM193 55gr.

That's just me. don't believe or use my numbers. Go out a get yours.

Have a good shooting!!!

yeah, this was only the first time shooting at 50. i plan to shoot more and, and have some BLM shoots coming up where i can have more freedom with distances. next time around i won't overthink it and just shoot the damn thing haha. when i can save more money i also hope to go to appleseed as well, probably with a 10/22 though since its cheaper.

thanks again guys