Hey guys,

I have been reading about the IBZ a lot on here. It appears that it was designed for the M$ which has a short barrel and the M193 55 grain round. If I remember correctly.

I have a M16A1 20" 1:7 twist zeroed with the 25m BZO. I really like the idea of the IBZ and would like to zero mine that way.

I can not find any definite info on how the IBZ would work with the A1 20" barrel. It seems that the thread always goes back to 25m zero with the A1. Also just for the curious, I want to do it because I like the flatter trajectory and do not want to worry and the "just hold ??" high or ??" low.

So can any of you gurus help me figure out the correct flight paths, zero point in yards using the "L" site to IBZ in at 200y with the M855 62 grain.


Thanks guys

The "L" sight and 25M zero was based upon the 250M/375M zeros of the M16 using M193 ammo.

Given the limitations of the original rear sight, I wouldn't use the "L" sight to zero at such close range as 200 yards when you have the other aperture.

The IBZ is for 200 meters not 200 yards and the easiest way to get a 200 yard zero is to shoot at 200 yards. Barring that, then try using the standard aperture at 58 yards for a rough zero, then confirm it at 200 yards. This way, when you rotate the rear aperture over to the "L" sight, it will give you a 335 yard zero, more or less.

If you want to zero at 50 yds, adjust your POI so it is ~0.25" below your POA,

If you want to zero at 25 yds, adjust your POI so it is ~1.25" below your POA.

As always, confirm at the range you want, in this case 200 yards.

Thanks. I knew that the IBZ was meters but wanted to do mine in yards which is what I am used to. The 58 yards is what I was trying to figure out. How did you come up with that number? Also can you explain why I should use the standard aperture instead of the "L" at 58 yards since you use the "L" at 25 meters when doing a BZO. I am just trying to learn so the reasons will help me understand.

Thanks again for the reply.

On the A1, using M193, the standard aperture was for a 250 Meter zero, rotating over to the "L" aperture made it a 375 Meter Zero.

If you use the standard aperture then you would zero at 42 Meters for a 250 Meter Zero.

If you did not have access to zero at 42 Meters, then zeroing the A1 was dirt simple. Here is something I posted 4 years ago.

1) Rotate rear sight so the "L" is showing.
2) Zero at 25M
3) Once zeroed, rotate the rear sight so that the std. aperture is showing.
4) You now have a 250M zero.

As always, confirm your zero by shooting at longer ranges.

The reason why you should use the standard aperture is because the "L" aperture is set higher than the standard one and if you use it to zero, when you rotate it back to the standard aperture, you give up the ability to extend the range of your rifle.

As for the whole 58/200 yard zero thing, you can input the data into JBM's website and find the answer.

(Sight height of 2.56", Muzzle Velocity of 3,100 fps, G7 BC of 0.150 [I've seen number from 0.148 to 0.151, so I SWAG'ed it])

Were this my rifle, I would just use the standard aperture zero at 50yds and be done with it.
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The IBZ was around for years before LTC Santose made it popular, just not in circles outside of AMU and is a very useful zero.

A couple of things, unless you really want a true retro rifle, use the square post A2/A4 front sight as it give a sharper sight picture. Also consider a 0.050" National Match front sight instead of a 0.070" standard one as it will subtend less (obscure less of the target).