AR zeroing

[45calibre]

I zeroed my ar for the first time today and i have a few question. I started at 25 yards and i had to move my rear mbus 13 clicks to the left to get my shots in the centerline of the target. This has left the aperature on the left side of the centerline hash mark on the mbus, Is it normal for it to be that way? Could it be my fsb is canted?

The upper is a 16" PSA CHF. I managed to get a really good zero at 25 yards and i was shooting about an inch low, which was good because ultimately i wanted a 50 yard zero and that is where the bullet trajectory places the bullet at 25 yards. I then went to 50 yards and i had a hard time seeing the center of the target. The best group i could get put my hits about an inch high, i decided to settle for that and called it a day. when i was shooting my groups i either had the stock totally collapsed or 2 clicks out, would having the stock retracted all the way out yield better accuracy since the peep hole will look visibly smaller?

 

[wsenefeld]

I typically have to go a couple clicks left but not as far as I think you're describing. Is your front sight on a free float rail or do you have a FSB? Your front sight might be canted. A mis-aligned free float rail or fsb could easily cause that, resulting in the severe windage adjustment. Is this a magpul mbus?

You might have a good 25 yard zero now but I'm thinking if you back up to 100 yards, you won't hit paper.

 

[sig1473]

I typically have to go a couple clicks left but not as far as I think you're describing. Is your front sight on a free float rail or do you have a FSB? Your front sight might be canted. A mis-aligned free float rail or fsb could easily cause that, resulting in the severe windage adjustment. Is this a magpul mbus?

You might have a good 25 yard zero now but I'm thinking if you back up to 100 yards, you won't hit paper.

You will hit paper @ 100yds(hopefully), but you will be ~5in high. Here is a good chart to follow.
View attachment 20034

 

[Kernal1984]

Ar15 Combat Zero - YouTube

This is a good video on different zeros that explains a lot.

Have my rifle zeroed at 200

 

[wsenefeld]

You will hit paper @ 100yds(hopefully), but you will be ~5in high. Here is a good chart to follow.
View attachment 20034

Bullet trajectory aside, I think the severe left adjustment of the rear sight will cause his point of impact to be a foot or more to the right of his point of aim at 100 yards.

 

[MCrupe]

Very helpful video Kernal1984 thanks for the share. I will be zeroing mine in at 25yrds some time this week.

 

[45calibre]

I typically have to go a couple clicks left but not as far as I think you're describing. Is your front sight on a free float rail or do you have a FSB? Your front sight might be canted. A mis-aligned free float rail or fsb could easily cause that, resulting in the severe windage adjustment. Is this a magpul mbus?

You might have a good 25 yard zero now but I'm thinking if you back up to 100 yards, you won't hit paper.

It is the A2 FSB, no free float rail. The rear sight is the MBUS.

 

[rvb]

Bullet trajectory aside, I think the severe left adjustment of the rear sight will cause his point of impact to be a foot or more to the right of his point of aim at 100 yards.

assuming there is a ~85mph crosswind, I agree.

If the sights (post and peep) are parallel to the bore [in windage], then the position of the sight body doesn't matter. It's just an aesthetics issue at this point.

Just be sure you have the rifle verticle when zeroing, if you have it canted, that could cause additional windage adjustment (and cause you to be off more at farther distances). You have to be way off veritcal to make a big difference, especially at 25 yds, but I thought I'd mention it. If that's not an issue, than don't worry about, imo. If it really bothers you, you could shim the rear sight to tilt it....

would having the stock retracted all the way out yield better accuracy since the peep hole will look visibly smaller?

You'll get the best results from the peep sights by getting the rear apperature as close to your eye as possible. If the charging handle bops you in the upper lip during recoil, you're probably doing it right...

An AMU Team member shooting prone....

-rvb

 

[223 Gunner]

The barrel may need re-indexed, which means you will have to send the upper back to PSA. I had this happen with 2 different Bushmasters, had to send them back to Bushmaster. I know this is a dumb question, but is the MBUS installed correctly? Windage adjustments should never be more than a few clicks.

 

[223 Gunner]

Also never use the large peep, always use the small one, it is much more precise.

 

[ViperJock]

I zeroed my ar for the first time today and i have a few question. I started at 25 yards and i had to move my rear mbus 13 clicks to the left to get my shots in the centerline of the target. This has left the aperature on the left side of the centerline hash mark on the mbus, Is it normal for it to be that way? Could it be my fsb is canted?

The upper is a 16" PSA CHF. I managed to get a really good zero at 25 yards and i was shooting about an inch low, which was good because ultimately i wanted a 50 yard zero and that is where the bullet trajectory places the bullet at 25 yards. I then went to 50 yards and i had a hard time seeing the center of the target. The best group i could get put my hits about an inch high, i decided to settle for that and called it a day. when i was shooting my groups i either had the stock totally collapsed or 2 clicks out, would having the stock retracted all the way out yield better accuracy since the peep hole will look visibly smaller?

My MBUS has several hash marks to each side of the centerline. Is your zero between the centerline and the next hash? If so you are probably fine. BTW did you notice if the zero started to right of the centerline cause that would affect how many clicks it would take as well.

I recommend you get a white paper plate and draw a cross through it with a black sharpie. Staple the plate to a larger piece of cardboard in case you are initially off paper. Its an extremely cheap target, and its very easy to see the center at distances exceeding 100yds. Changing your head position will affect your zeroes, find one and keep it and then adjust the stock as needed for different shooting positions to keep your cheek in the same place.

Finally, I like to zero my ARs at 100yds unless I am planning to do mostly longer range shooting. A zero on 100 and aiming at center of mass you will hit a man size target in the torso from 25-300yds. For more precision shots you can hold up. If I was gonna shoot 90% of my time at 25-50yds then I'd zero at 50. Having sites that you can adjust for elevation easily changes that. As a Rule I like to put my zero on the highest point of the trajectory that I plan to use. Make sense?

 

[Hop]

There is some play in the barrel pin to upper locating slot. Your A2 FSB might be canted. My Colt was canted (my fault no theirs). Does the gas tube look centered inside of the hand guard? Some hand guards, like the Magpull MOE, have slots so it's easy to tell.

 

[ATM]

Bullet trajectory aside, I think the severe left adjustment of the rear sight will cause his point of impact to be a foot or more to the right of his point of aim at 100 yards.

That would not be the case.

 

[45calibre]

I am pretty sure that the MBUS is on correctly and the gas tube looks straight under my moe handguards. There was no wind that day at all. this is how i had to set the sight.

 

[wsenefeld]

That would not be the case.

How so? You find zero by intersecting the bore plane with the sight plane. Once you go past the point of intersection (25 yards in his case), the sight plane moves away from the bore plane. Similar to mounting an optic on top of a carry handle, the further your sights or optic from the bore plane, the greater the variation at distance. If he has his rear peep maxed out to the left, I believe he'll be further and further right when past 100 yards.

 

[wsenefeld]

I am pretty sure that the MBUS is on correctly and the gas tube looks straight under my moe handguards. There was no wind that day at all. this is how i had to set the sight.

I think you're fine. Looking at the bottom of the mbus, it doesn't look centered on the rail. Your rear peep is probably centered and your front sight not canted. The rear sight body itself may not be truly centered when mounted.

 

[45calibre]

the bottom of the mbus looks centered to me.

 

[rvb]

this is how i had to set the sight.

doesn't look that bad....

How so? You find zero by intersecting the bore plane with the sight plane. Once you go past the point of intersection (25 yards in his case), the sight plane moves away from the bore plane. Similar to mounting an optic on top of a carry handle, the further your sights or optic from the bore plane, the greater the variation at distance. If he has his rear peep maxed out to the left, I believe he'll be further and further right when past 100 yards.

the front sight, rear sight, and center line of target should never leave the same vertical plane when we are talking windage. If they are lined up at 25yd, then they are lined up at 1000 yds. Any adjustment is due to spin, wind, not holding vertical, etc. Just because the apperature sits off-center of the site body doesn't mean the bullet is going left to right.

If the FSB is angled to the side, and we adjust the rear accordingly and still hold the FS post verticle, the bullet doesn't know the difference.

I think the severe left adjustment of the rear sight will cause his point of impact to be a foot or more to the right of his point of aim at 100 yards.

That's the amount of lateral impact change you see with the gun SIDEWAYS (eg shooting under something low). If the irons are ~2.5" tall, then a 25yd zero and the gun sideways would result in approx 7.5" of shift in point of impact at 100 yd. (roughly -2.5" at point blank, on at 25, 2.5" at 50, 5" at 75, and 7.5 at 100).

-rvb

 

[ViperJock]

How so? You find zero by intersecting the bore plane with the sight plane. Once you go past the point of intersection (25 yards in his case), the sight plane moves away from the bore plane. Similar to mounting an optic on top of a carry handle, the further your sights or optic from the bore plane, the greater the variation at distance. If he has his rear peep maxed out to the left, I believe he'll be further and further right when past 100 yards.

This would be true if the sight were not actually aligned but slightly off to the left. In that case the MOA in which the POI is not zeroed would be magnified at increasing distances. Meaning that if he were 0.25" Left at 25yds, he would be 1" Left at 100yds, 2" off at 200yds and so on. The sight plane affects elevation even with accurate zeroes. A zero at 100yds would have a gap between the sight plane and the bore plane with the bore plane being lower and thus the POI being lower than the zero.

 

[tetsujin79]

Just weighing in on the MBUS for some ... I bought a FS, and as soon as I mounted it, it wouldn't flip up from the left or sit flush. I returned it, got another one which laid flatter, but not flush, and still would not pop using the left tab.

So for my experience Magpul has build specs that have some play in them and my railed hand guard (Troy VTAC) picatinny is too wide/out-of-spec. I've decided that my rail is the bigger issue, since the rear sight slides right on and off of the upper, but is too snug on the hand guard.


As for the windage, I found that with the detachable handle I had, mounting and re-mounting with different ways of tightening the screws would change how much windage I needed to zero the rifle.


So, if yours slides around, maybe it's torquing in the picatinny when you tighten it down and throwing your windage off?