Understanding Zeroing

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Phoenix54c

New member
First & foremost, hi! It's nice to find such a seemingly congenial gun forum.

This question is about the zeroing process. After combing several forums, I understood that any .223/5.56mm rifle firing a certain load (55/62gr @ ~3200 fps) could be zeroed at 25 yards in order to make the bullet cross the barrel's axis again 300 yards later.

Now, I am not so sure. I am now questioning whether this data only applies when the rifle is of a certain make, the sights are of a certain height, and the barrel at a certain angle.

Given the my sights' height above bore is taller than a standard AR-15, does this mean AR-15 sights with ranging functions will not be accurate for me? Will the 25/300 or 50/200 zero paradigms work for me?

I'd appreciate any help, because I'm very confused at this point.
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Beretta ARX
0-200yd sight aperture are 3.75" above center bore (roughly)
16" 1:7 twist barrel
 
First, welcome to the forum.

You are correct to believe that the height of your sights from the bore will change the distance at which your bullet will cross the line of sight again. However, there are many factors that play a part in determining your actual zero distances. You never know how your gun will shoot until you shoot it at those distances. That is part of what keeps this so interesting. Just when you get a load figured out some new bullet or cartridge shows up to tempt you into starting again.
 
Yeah, in the final analysis, the only way to truly verify the data is to shoot 'em and see where they land.
A ballistics physicist told me that.
 
The best way to establish a zero is to shoot the rifle at every range (distance) you plan on shooting, then write it down and tape it to your rifle's buttstock.
 
OP is correct that this sighting approach is somewhat dependent on sight height above bore. With a 1.5" height above bore, you can indeed set your sights to a 25y zero, have the bullet pass about 3" high at 100y, and have it come back to zero near 300 (JBM says 290 for one particular load).

If you have taller sights, you can achieve the same effect with less sensitivity to sight height by zeroing 3" high at 100y. I tried that with a 2" high sight, and it basically didn't move the 2nd zero distance. If I'd zeroed with e 2" sight height at 25, I'd be way off.

You can also measure your height above bore and use a ballistics calculator that has height above bore as an input to make your own appropriate zero scheme. The "maximum point blank range zero" feature may be of use: http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi
 
There are many variables.
There are ones you can't really control, like wind, humidity, elevation, temperature, etc. The will impact your bullet's trajectory.

The ones you can control are things like bullet weight ballistic coefficient (determined by the cartridge), velocity (cartridge and barrel), sight height, presumed "zero" (must test to find out if your data is accurate).
 
The online ballistic calculators are a good place to start.
With a 3.75" sight height, you'll probably want to be about 2 to 2.5" low at 25 yards.
 
any rifle can be zeroed at 25 yards in order to make the bullet cross the barrel's axis again 300 yards later.

Where the ballistic and other factors (bullet, velocity, sight height etc) come into play is in determining where on a 25 yds target the bullet should strike, relative to your aiming point.

As an example, in the mid 70s we "battle sight zeroed" our M16A1s at 25m, shooting the then standard 55gr FMJ load. This (we were told), would put the rifle "on" at 250m.

There was an aiming point in the center of the 25m target. There was an "X" on the target a few inches below that, where the bullets would strike, when it was properly zeroed. And it worked quite well for dropping the 250m popup targets.

The principle applies to all rounds and sight combination. Each one has a spot where it works. Change something (gun or ammo) the spot moves, and must be recalculated, or determined by actual shooting.

I can't tell you how to calculate it, but I can tell you how to find it by actual shooting. Sight your rifle to hit exactly point of aim at the desired distance (300yds or whatever). Then put up a target at 25 and shoot. Measure the distance between the bullet strike and your point of aim. Write it down. Now you know how much below (or above?) point of aim it is at 25yards for that load from your rifle. Change anything, and you can still use the known measurement as a reference point.
 
kraigwy wrote:

The best way to establish a zero is to shoot the rifle at every range (distance) you plan on shooting, then write it down and tape it to your rifle's buttstock.
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Ditto!!!

I've only had one rifle that would shoot the exact bullet with a chronographed velocity within +/-1" of the 100 yds stepped ballistics trajectory to 500 yards. All the rest were off enough to warrant shooting each distance.

PS: I tape it to the scope
 
I understood that any .223/5.56mm rifle firing a certain load (55/62gr @ ~3200 fps) could be zeroed at 25 yards in order to make the bullet cross the barrel's axis again 300 yards later.
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At least at one time this was the method used in the military using military issue ammo in military issue 20" barreled rifles. The problem was that you are about 4-5" high at 100 yards and 10-11" high at 200 yards with this method.

Using this method meant the rear sight could be adjusted to be zeroed out to 500 yards. Since the military is now issuing optics mounted on shorter barreled carbines and heavier bullets I don't know what they are doing.

It it were my rifle I'd zero at 100 yards, plug the data into a ballistics program to get an idea where you'll be hitting at various ranges and then fire at those ranges to confirm.
 
I came from the old school of teaching to zero 223/5.56 55 gr bullets at 25 and 250.

Not just ARs but for 223 Bolt guns.

The 25/250 zero will allow you to shoot 40/40 on the Army's 300 meter qualification course. It makes a near perfect BSZ for the M193 ball 5.56.

After Vietnam the Army Marksmanship Unit took on the task of continuing sniper training. Hardly anyone else was doing it.

The AMU Sniper School provided cadre for the Secret Service, FBI, and untold Civilian Police Departments and even the Marines.

At the time the AMU was recommending a 223 Bolt gun using a fixed 6 or 8 power scope.

They taught the theory of sighting in the LE sniper rifle at 25/250 where as you can make head shots to 300 without hold over/under. Civilian LE would have little need shooting past 300 yards.

It worked. I started a program for our PD, I taught rifle marksmanship, including sniping to the Anchorage Police Dept. when they started their SWAT program.

I also carried a sniper rifle as a LE sniper/counter sniper. It was in fact a Remington BDL Varmint in 223 with a Redfield Widefield 6X scope. I sighted it in for 25/250 and guess what it worked.

In reality, a 250 zero with the 55 grn M193 will be about 2.1 high at 100, 2.8 at 150, 2.3 at 200 and down 2.9 at 300.

I didn't just accept that zero recommendation, I tested it un-teen million times.

When I taught LE snipers I took them to the Army's 300 meter qualification course but we only counted head shots. The 223 would do it. My rifle will still do it, though the scope I used in 1978 is dark and milky now, but the gun ammo still does it.

Am I saying that is the one and only method of zero, of course not. Its not the zero I use on my ARs (or not all of them anyway)

My service rifle White Oak AR sights bottom out at 200 yards. I'm good for the comeups I need to shoot service rifle to 1000 yards.

But at close range it shoots higher then I want at small targets under 100 yards in 3-gun events.

Where I shoot 3 gun the max range is 50 yards. At 25 yards I need to come up 7 1/2 moa clicks, at 35 I only need 2 up, at 15 yards I need to come up 19 - half moa clicks.

I shoot irons and the height of the carrying handle sights will screw you up if you don't pay attention. Under 100 yards ARs can be tricky if you're shooting golf ball size or smaller targets.

So in the walk through before the stage, I measure the distance to all the targets and write down the come ups I need.

No substitute for confirming any and all zeros and writing them down.

I said it before and I'll say it again, one of the most critical tools used in any shooting is a well kept data book.
 
Got me curious, so I ran some numbers in JBM, looks like zeroing at 45 yards should give you a 300 yard far zero, using the velocities for 55gr and 62 gr ammo from a 16" barrel published here.

Of course you should reality check this at the range.

On edit: For bullets in JBM I chose "Winchester USA Full Metal Jacket" from the list.
 
Hey everyone! I've been out of contact for a long time and am just getting back to this. I had a chance to put all of this info to use today, and appreciate the feedback & explanations from all of you. Your insights were very helpful, and I want to summarize it for anyone who comes after me.

I was confused about zeroing, because I did not understand the notion used to describe it. For example, I see people describe different zero configurations in the format "x/y" (for example, "25/300" or "50/200"). Mistakenly, I thought that "x" and "y" were distances for which point-of-aim equaled point-of-impact. I now see this isn't quite the case.

"X" simply represents your distance from the target you are using to make your adjustments. This number is usually limited by the short length of most civilian ranges (25-100 yards).

"Y" is the actual "zero" distance, i.e., the distance at which point-of-aim = point-of-impact.

So, the challenge is "guessing" how you need to adjust your sights to zero at a certain distance, without actually having that distance available to you. In order to do this accurately, you have to know something about the trajectory your bullet will take from your muzzle. This trajectory is a factor of many things, like your sight height, shooting angle, type of bullet, etc. However, once you have the trajectory, you can make a pretty darned good guess about how to adjust your sights so that they are zeroed at a certain distance. For example, let's say that a ballistic calculator says that my rifle should hit about -2" at 25m when zero'd for 300m. In this case, I would merely need to move my target out to 25m, aim right at the bullseye & adjust my sights so that the bullet impacts 2" below it. I would then have configured my rifle for a 25/300M zero.

I hope I got that all right. :cool:
 
No, "25/300" or "50/200" are actually zero distances.

With a 300 yard zero, based on the numbers I ran when you first posted, your rifle should also be zeroed at 45 yards. The 25/300 meters is for a AR15/M16 with A2 sights, your sights are higher above the bore, so the relationship between your line of sight and bullet path are not the same.

This is generally referred to as near zero and far zero. At 45 yards, the bullet is rising in relation to the line of sight. It will be above the line of sight from this point, still climbing until it reaches the apogee, 4.8" high at ~180 yards)when it starts to drop, to when it crosses the line of sight again at 300 yards.

sightLine.gif


More detail on the concept here: http://ballistic.cs.umd.edu/ballisticsBackground.html
 
As a hunter, I sight in most of my centerfire rifles for 2" high at 100 yards. That's right at dead-on at 200 and roughly 6" low at 300.

I've found that, depending on the height of the sight(s) above the barrel, 25 yards is merely a starting point for checking group size and sight-in at 100 yards.
 
No, "25/300" or "50/200" are actually zero distances.
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Okay, I'm reading you now. That graphic helped visualize how the round travels. Thanks for that.

The ARX has a diopter sight; assuming it is sighted-in correctly, then I should be able to set it to "300m" & hit close to center at about 50 yards.

Setting it to 400m should cause it to strike about 1.6" high at that same distance, with the near zero being approximately 25yards.

I'll try this out at the range this weekend and post back with my results. I appreciate the explanation. As you can see, this subject confuses the heck out of me. ;)
 
Some of my rifles are zeroed at 100.
Most are zeroed at 200.
One is zeroed at 300.
Several are zeroed at 400.
6 are zeroed at 1k.
 
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