25 meter sight in?

[txgunsuscg]

The book you are referring to is the DOPE book (Data On Previous Engagements), and it is exactly what it sounds like - a running log that documents their shooting at various ranges, under different environmental conditions, even the lot number of the ammo they used. From the logged shots, they pull information that helps them judge their dope for the cold bore shot. It's part science, and part art.

For my rifle in 5.56, I hold over for under 25 (between 1-3 inches), and under for between 26 and 299, usually between 3-6 inches. Because of the bullet's trajectory, which is an arc (in order to defeat that d*** gravity), the bullet "rises" from 0-25 where it crosses the zero, and continues to rise through 100 and 200 (the rising branch) until reaching its highest point (max ordinate, usually between 2/3 to 3/4 of the way to the target), and then falling (falling branch) until it crosses zero again at 300.

 

[henschman]

I know it was assumed in everybody's post which rifle we're talking about here, but since the OP didn't mention it, I want to clarify that the 25/300m zero is only for an AR-15 with a fixed carry handle and standard issue 55 grain M193 or 62 grain M855 ammo. Any other rifle will also have a "second zero" if you zero it at a short distance like 25m, but where that second zero is will depend on the height of the sights above the bore, the velocity of the bullet, and the ballistic coefficient of the bullet.

For instance, on an AR with a detachable carry handle, the sights are actually a little higher above the bore than on a fixed carry handle rifle... so with a 25m zero, the second zero is actually a 320m zero or so. That is why the detachable carry handle rear sight has a little "z" mark 1 MOA higher than the 300m setting on the elevation drum. If you zero the rifle at 25m with the rear sight set on the "z" mark, you have to adjust it back down one click to get to your 300m setting.

All this is done with the small aperture. The big aperture is 2 MOA lower than the small one, so if you are zeroed at 300m with the small aperture, flipping to the big one gives you a 50/200m zero.

 

[Texan Scott]

Most of us who were issued M-16s and taught the 25-300 yd zero thing prob. realize that the military in general is not overly concerned with shot groupings by the average serviceman. As long as most of us shoot well enough to hit the enemy somewhere most of the time, and they throw enough of us at the problem, we stand a good chance of winning.

This has never seemed satisfactory to me, either as a man who wanted to survive a combat engagement at rifle range (which never happened to me- airstrikes are called in best when the target doesn't know you're watching ) or as a man who wanted to put meat in the family freezer with minimal fuss.

I would still sight in a new rifle at 25 yards first, but only to be sure i'll be on paper at 100yds. if i were shooting a 300 yard rifle, i'd sight in at 25 to be on at 100, then sight in at 100 to be on at 300 (because nothing i've ever hunted with shoots NEARLY as flat as 5.56 ball).

Somebody on THR (apologies, don't remember who)has this sig line: "In theory, theory and practice are the same. In practice, they aren't."

^^ this is an astute observation. ^^

 

[Old Dog Man]

25 & 300 sight-in

I have sighted in many rifles in my years, I always start at 25yrds. to get on target (saves customer money). Starting at 2-3" low, have had some shoot low at 100yrds. and some shoot very high, you should try your rifle and ammo and find out for sure what your set-up will do. Al

 

[DPris]

My uniformed days are behind me, I am not interested in either military or LE engagements anymore.
For MY purposes, I want to be able to hit an approximately grapefruit-sized target out to a max of 200 yards, using basically the same sight picture & hold. That'll handle rabbits at 100 and coyotes at 200 without much guesswork.
I want to reduce the guesswork.

If my guns are zeroed at 25, it reduces my chances of being able to use pretty much a center-point aim, or a point-blank aim, at 100-200 yards.

If I zero my guns 2 inches high at 100 yards, I can use pretty much the same center of mass (and that's a SMALL center of mass, not a human torso-sized center of mass) hold from 100-200 yards, with a much higher hit probability.

My goal in zeroing is to reduce making guessworked physical adjustments by having to move the sights as distances increase any more than I have to.

In the four ARs I tested from 25-200 yards, the degree of bullet "rise" at longer distances varied between bullet weights from gun to gun, barrel lengths from gun to gun (velocity variations), and sight types (standard carry handle, and three different optics).

In my own testing, in my own guns, I found the 25-yard zero's chances of striking a grapefruit-sized target inferior to a longer zero's chances, using the same sight picture.
If I zero at 25, I HAVE to aim lower for a 200-yard target. If I zero for that 2 inches high at 100 yards, I don't.

Those are my direct experiences in real life with my guns & different loads, and they are the reason that I'll continue to zero my ARs that way.
I zero long to strike long.
Denis

 

[henschman]

With an AR, if you want to hit more like grapefruit-sized targets at closer ranges, from your 300m zero, just flip to the big aperture. That is a 50/200m zero, and will only be off a couple inches either way from point blank out to 230m or so.

 

[DPris]

If I were using an aperture...
Denis

 

[lloveless]

I zeroed my DPMS LR308 at 25 yds. It then shot 6 inches high at 100 yds. Tomorrow I'll change that to a 3 inch high at 100. This is in a 16 inch barrel and 150 gr bullets.
ll