How much does the increased height over bore affect the 36 yard zero and 50 yard zero?

Try putting your information into JBM Ballistics (free online), and it should show you what the changes do.

It’s going to depend on your barrel length. A 50/200 isn’t exactly true when you run a shorter barrel.

There are a lot of variables, bullet wieght, barrel length, twist, etc.  But here is a typical chart for standard sight height, 55 grain 5.56, 50 yard zero



And then 1.93



Same load with 36 yard zero, standard height



And 1.93



The taller sights really skew the downrange ballistics when you use the shorter 36 yard primary zero.  The taller sight essentially turns the 50/200 into a 50/250

For Unity mounts I find a 75 yard zero is fantastic.

A 2.26 unity mount puts the sight 3.475 over the bore.

A 25 yard zero with 55 gr ammo going at about 3100 fps will put you on at 25 yards, 3.2 inches high at 50, 9 inches high at 100, 16.9 inches high at 200, and 18.7 inches high at 300.

A total garbage zero. It’s the most common I see people use at indoor ranges with these mounts. These people have no clue where they’ll be hitting at distance. They’ll totally miss the target once they leave their indoor range.

With a 36 yard zero, you’ll be 1 inch low at 25 yards, 1.2 inches high at 50, 4.9 inches high at 100, 8.8 inches high at 200, and 6.6 inches high at 300.

Not very good as you can see. While it’s not as bad as the 25 yard zero, it’s still almost unusable.  

With a 50 yard zero you’ll be 1.6 inches low at 25 yards, on at 50, 2.5 inches high at 100, 3.9 inches high at 200, and 0.7 inches low at 300.

As you can see, 50 is much better. You’ll still be up to 4 inches high at some distances which you’ll have to compensate for that you wouldn’t have to compensate for with a normal height mount.

A 75 yard zero puts you 2.1 inches low at 25, 0.9 inches low at 50, 0.6 inches high at 100, 0.2 inches high at 200, and 6.2 inches low at 300.

This is the flattest zero from 0 to 200. It’s the most usuable. At 300 all you would have to do is aim one dot high. Even if you forget to, you’ll still hit low on a chest. This is the zero you want. If you can’t get good groups at 75 yards with your dot, use a 50 yard zero instead.

I will be using MK262 from a 12" barrel but I understand M193 is very close.

This is all great information.  Thanks.

I just ran those numbers. An Mk 262 from a 12.5 inch barrel goes at about 2550 fps and has a ballistics coefficient of .373 according to another thread I found on here.

It‘s close as you said but there are some changes.  

With a 36 yard zero, you’ll be 1 inch low at 25 yards, 1.2 inches high at 50, 4.3 inches high at 100, 5.6 inches high at 200, and 0.8 inches high at 300.

With a 50 yard zero you are 1.6 inches low at 25, dead on at 50, 2 inches high at 100, 1 inch high at 200, and 7.8 inches low at 300.

With a 75 yard zero, you are 2 inches low at 25, 0.8 inches low at 50, dead on at 75, 0.4 inches high at 100, 2.2 inches low at 200, and 12.6 inches low at 300.

I’d pick the 50 yard zero for that load since it seems to be the flattest.

Thanks again.  
It looks like 36 is the flattest (approx 6.5" spread to 300).  50 is the flattest by far out to 200 (Just over 3.5" to 200) (approx 9.75" spread to 300)
I think you may be right with 50 being the best but living out in the desert makes it a tougher choice.

You could also use an MPBR calculator (if you have good data on *your* stuff) - give it a target zone diameter and see what it says.

The 5.6" midrange apex with the 36 yard will mess with your holds more than holding over on targets beyond 200 with the 50.

So this is why I would choose a 50 yard zero. A 36 yard zero will be on at 300 but at 100 which is a more likely shot, you’d have to compensate by shooting low since you’ll be 4.3 inches high. At 200, you’d have to compensate by shooting even lower since you’ll be 5.6 inches high. If someone is shooting at you from behind cover where only their top half is exposed, it could be a miss if you don’t compensate.

With a 50 yard zero, you’ll only be 2 inches high at 100 and 1 inch high at 200. You won’t have to compensate at all. Just point and shoot with no compensation out to a little over 200 yards.

A 300 yard shot which is rare is the only one you’ll have to compensate for by holding one 2 MOA dot high. Just one dot of hold over will score a hit since holding one dot high at 300 will raise your shot 6 inches.

A 50 yard zero is point and shoot with no guesswork whatsoever for hold overs or hold unders out to about 225 yards. 250 yards and more is the only hold over you need and it isn’t much. Just one dot of hold over.

With a 36 yard zero you’ll have to hold under multiple dots at 100 and 200 yards.

Great data everyone.  Thank you.

I plugged in a 50 yard zero with a BC of .373 (77 SMK), 2550 velocity (12.5"), 3.471 optic height (Unity), 5200 altitude, and a maximum 5" target for point blank range.  

Far zero is 224 yards
Maximum PBR 258
8.1" low at 300
26.7" low at 400

Academic theory is great an all, but how often, especially as a civilian, will you be engaging in firefights at 300, 400+ yards.

I like 100 yard zeros. None of this above at X yards, below at X yards.

Never. The only time anyone will engage at that distance is if there is all out war where one is part of team and engaging anyone carrying a weapon wearing a different uniform than yours.

Not everybody owns an AR just for engaging an enemy.  The 50 yard zero is about the best there is to get a point blank out to 225, or a little more depending on load.  The bullet stays within a couple inches of line of sight so even small targets like 'yotes or gophers ar dead on holds.  For a scope that has reticle information that requires a 100 yard zero it is another story.

People who actually shoot with 1.93” + mounts know this to be true.

That’s almost like a 75y zero with a Unity and an SBR. 75 is a little flatter for longer than a 100y zero. Either way everything is holding high.

Which scope are you running? Specifically, which reticle? Get a program like Strelok. I zero for 50 and confirm at 200. That puts me shooting pretty flat out to 200 and once confirmed, I use the holds in Strelok. The program will correlate holds according to your reticle. The more accurate you are with your bullet speed, the more accurate the program is with regard to your reticle.

This is an example of what it looks like for my 12.5 rig with a TA31F.

You’re not taking into account the height of the mount. The Unity mount is going to give you a height over bore of ~3.48”. For comparison, this is a 75yd zero with M193 from a 12.5” barrel (2818 fps avg). I’m using a MI NV-height mount (2.33”) so my height over bore in Strelok is 3.55”. The difference in zero between 75 and 200 is less than the value of one click of elevation.

I made a pretty in depth excel sheet for zero distances on various barrel lengths and optics heights. Here's what I have on Mk262 on a 12" bbl.

25, 36 and 50 yard (or meter) zeroes are intended to get you on paper at distance. Final zero should be done at full range.

Thank you!

You have me intrigued to try a 75. I have always done 50 using the targets that Kinetic Consulting created which allows you to zero for 50 at 10 yards. Might have to try 75 though.

For me, the goal is to have the widest span of distance I can get with a dead-hold, and impact within around 1.5" elevation of point of aim.  I have found that the 50/200 zero best achieves that goal.  If you are ok with a wider accuracy band than 1.5", then you can deviate from that more.  But in my assessment, attempts to get the CQB zero more accurate tend to result in a very small span of distance yardage that actually hit that zero, and very huge deviations from zero once you get outside that.  Which is to say, a 10 yard zero, makes the rifle  all but useless for any distance other than 8-15 yards - for example.  What I have found is a 50/200 is a good primary sight zero,  and run something secondary like a laser, for much closer.

The problem is, the 50/200 falls apart when you factor in the height of the Unity (or in my case, MI-NV height) mount. At that height over bore, it turns into a 75/200

Or a 50/250.  But yea, optic height raises he'll with all of these primary/secondary zero numbers.  And, how many weekend 25 yard indoor range warriors have actually stretched their 25 yard zero out to see where they actually impact at distance?  Damn few I expect, from what I read on this board.