Howdy all.   Need your help with a quick question.

Been a long time since I've sighted in one of my ARs, but iirc when you sight in at 25 yards you want the rounds centered on the paper and one inch low to hit the target center at 100 yards.  Is this correct?  Oh, if it matters, I'm using either a 55 or 58 grain bullet.

The indoor range I shoot at is limited to 25 yards, and I want it centered at 100 yards so I need to do the adapt, overcome, improvise thing to center up my hits.  Don't care about further than 100 yards as I can't see the target after that!!    

Did a search but the search engine only allows a 30 day max look back and didn't find anything specific to my question.

Thanks

Mike

What you want to do, if you only have a 25 yard range to zero on, and you have a non-elevation-adjustable rear sight, is to set your sights where your projectile impact is about 1.1 inch low at that distance. This will equate to a 50 yard zero.

Using a 100 yard zero is generally called a "bubba zero", and will result in the round dropping quickly after 100 yards... limiting you completely unnecessarily.  

The 50 yard zero is a much better, more efficient one, and will have you hitting slightly high at 100 yards so that you'll be hitting right on out at around 200 meters, and the bullet will never go more than a couple of inches above or below your line of sight anywhere between about 10 yards and 250 yards.

Here's a great thread on how you really want to set up your rifle:
http://www.ar15.com/forums/topic.html?b=3&f=18&t=328143

Although that thread is partly focusing on how to set up an A2 sight in order to get the RIBZ zero while retaining the ability to use the elevation knob correctly, the bottom line is that the proper "battle sight zero" will have you shooting point of aim/point of impact (zero) at 50 _yards_, which will result in your "far zero" (where the bullet drops back to the level of the sights and then below it) occurring at about 200 _meters_ (219 yards).  This results in a very flat trajectory that will let you shoot the nads off a gnat, so to speak, from the end of your barrel out to about 250 yards.

At any rate, to restate things, if you're using an A2 type sight, use the info in that thread to set it up properly. Otherwise, if you're using a backup type rear sight that doesn't feature elevation adjustments, just set it so that at 25 yards the projectile is hitting 1.1 inches below your point of aim.

Edited to add: This zero will put you about 1.5" high at 100 yards. Certainly nothing worth worrying about since standard GI spec ammo is only gonna get you about a 2" group at that distance at best.

Don't do it -  shoot to 25 yds like the book says. If you have some kind of optical sight, you can zero that at 50. If you zero at 50 with your irons, the elevation knob ranges will not be synchronized unless you make the 'Santoz' modification. Then you may well find that your front sight post isn't tall enough and you have to get a new one. I did this, then put it back to original and zeroed at 25. You'll be higher at 100 than you would with the 50 yd zero, but you'll still get a 'kill' on a torso target out to 300. It's actually stupid to take a weapon that is designed and built for a certain targeting then manage to defeat it.

To the original question, no, you will not be 'on' at 100 yds whether you zero at 25 or 50. Both targeting schemes have a trajectory that is several inches high at 100.

from my Ballistics program:

-0.85 inchs at 25 yards will give you 1.89" high at 100 yards, dead on at 200 yards,  -4.47" at 250 yards and -12.23" at 300 yards.

This is for 55 grain bullets at 3240 FPS - standard military load

Unless of course that "torso" is 100 – 300 yards away and below ground because the bad guy is shooting at you from a fox-hole with only the top half of his head exposed.






mbsigman, you can achieve a rough 100 yard zero if you adjust your sights so that your point of impact is approximately 1.5” low at 25 yards.

These guys have given you some good info. I'm gonna make mine short and sweet. I set my irons and EOTech to be zeroed at 50 yd. From what my research has told me set it for 50 yd and you will be dead on again at 200 yd. So if all you have is 25 yd set it roughly an inch low and you'll be gtg when the zombies invade.

It's all moot, zombie engagements are always within 50 meters anyway.

Well incase you scout out a hoard at 200 yrds you can get a head start.

Many thanks, especially to Mr Molon, for the replies!

There's a 100 yard outdoor range that I can get to, but 100 yards is it.  Although the rifle is no doubt capable of going way beyond that accurately, t'ain't no way I can!!  100 yards is plenty for me, and then I do the Monty Python thing:  RUN AWAY!!  

All kidding aside, I sincerely appreciate everyone who took the time to share the info.

Mike

Look at the graphs Molon posted. Zeroing at 50, only makes you about 1.5" high at 100 yards (less than the size of an average group with mil-spec ammo), and the zero will make your rifle MUCH more versatile. You know the old saying... "better to have it and not need it than to need it and not have it". That applies here nicely. Zeroing dead on at 100 will only limit what you can do, while putting the center of the group that 1.5" above center will dramatically improve what you can do with the rifle if - God forbid - you ever had something unexpected happen where you _needed_ that extra distance. Think about it. 1.5" is not more than about the distance from the bottom of someones nose to right between their eyes. That's a really small difference at 100 yards when using irons, so you gain a more effective zero without having _any_ real trade-off.

Just think about it a while, and you'll see the logic. Everything I just said came from Molon's RIBZ thread and the original IBZ discussion years ago back on the old AR15-L email list. This is not some wild theory. It's quite well proven.

But hey, I don't mean to be going on about it if you're dead set against it. I've said my piece. Just trying to be helpful.  

FWIW, many serious folks pulling triggers in nasty places around the world have adopted the 50 meter zero for precisely the reasons outlined above. Say what you want about the "stupidity" of not using a weapon system as designed; in my world it's far more stupid (and deadly) to refuse to adapt and improve when a better mousetrap comes along. Cheers.

All I know is that we did our final zero at 25M in Kuwait.

The more I read on this the more confused I seem to get.  With some help I could actually understand this I think…

I have a Millet DMS 1x4 mounted in a CAA one piece.  Its about 1.6" over bore.  I sighted it in at 50 then took it to a different range and it shot 6" high @ 100!

So I resighted it to 100 and have shot two carbine matches with it and did fine*.  *When I did my part, bullets went in the right places. I.e. I was able to hit reduced torso steel at 177 yds last weekend under the clock using a 2” drop from POA.  And consistently shoot 2x4” targets at 8-15 yds with ~ 1-1.5” hold over.

Questions for the smart guys

1) Six inches high?  Why?  A match AR shooter at the range attempted to school me on height over bore, POA vs POI, laws of convergence and never cross the streams etc.  It did not help much.  I do understand the concepts though, he just went too tech too fast.

2) I handload and I use the Hornady ballistic calc, but think I may be reading it wrong.  I also use handloads.com calc.  My 55gr reloads typically cruise about 2850 with BC of ~.243.  I can get 2 MOA from mine and the 6 other guys guns that are using these reloads, so it works for just about any shooting practice we attempt.

BTW Handloads.com says 50 zero for the above set up = -0.6” @25 and +.26” @100   out to -3.66” @200.  Also shows 25 zero = 2.69” high @100

3) I have read many of Molon's post on ammo testing and learned a ton, but it looks like his height over bore is 2.6-2.8 inches in his ballistic chart.  What sits that high?  Ultra high rings?

4) Does the 50y/m sight method work with optics just as it does with irons or is there some parallax alternate universe thing going on here?  It seems to work fine for my other rifle, an EOTECH /ARMS 40 combo.

Can somebody school me on my dope?

I'd really like to sight the Millet in @ 50/236ish as I understand the + - 2.0" is ideal for most "practical" shooting.

Many thanks

I think your over the bore height may be incorrect. Double check your measurements. PS: A2 irons are around 2.6".

RIBZ

Revised Improved Battlesight Zero


I did this and am very happy with the results. A close range gun is more practical for me and this allow adj from 25 on out.

Thanks.  Seems awfully simple now doesn't it.  I was only taking into account the mount and scope hieght.  Not the flat top over bore measurement.  Guess I've been lucky in my shooting, but I see the differences are not that extreme.

Still don't understand the 6" change from one range to another, unless on the first I was shooting downhill a little...

We use a 50 yard zero on all of our work guns, but we use a modified target and aquire this 50 zero at 25 yards.  Works quite well.  Should you chose to use a 50 yard zero, it could easily be accomplished on the 25 yard range.

ETA: I just looked at one of the targets we use.  Using these targets, you can also establish a 100 yard zero shooting on a 25 yard range.  I have not tried this, and would check the rifle at 100 yards after doing this four sure, but the 50 yard zero works quite well, so I would have to assume that they figured them out for 100 yard zero as well.