Why the 50 Meter Zero? (rifle marksmanship)

Total Survivalist Libertarian Rantfest ^ | 5/1/13

[LibWhacker]

Why the 50 Meter Zero?

Rourke linked to an excellent pictorial about ballistic trajectories from different zero's over at M4.com.

Let's look at the trajectory using a 25 meter zero.

If you look the bullet path is 8 inches high from roughly 125m to250m. This is a real problem. This is enough of a problem that folks will miss targets. In fact that is what happened.

My informal understanding of the development of the 50 meter zero is as follows. Dudes were missing Tango's in the 100-150 meter range which was pretty close to the max range guys found themselves fighting at in Iraq (yes there was that occasional long tail fight which was further but lets not get into the weeds). After some consideration, or quite frankly I'm not quite sure what, the SOF community began to transition to a 50 meter zero. This trickled to varying degrees into the conventional Infantry guys and the shooting community at large. That is how the 50 meter zero came about in my understanding. If anybody (John Mosby, K or Lizard Farmer come to mind) has a better understanding of that development through something other than reading on the interwebz I would be interested in hearing it.

So let us look at the 50 meter zero.

As you can see this zero is much flatter. From the muzzle out to 250 yards or so (varying slightly by barrel length, twist, etc) the bullet is at +/- 2 inches. This is what matters. Granted I might need to hold over a little bit at longer distances but inside 250m it's just muzzle on target, relax, squeeze trigger. Since the vast majority of military engagements happen well inside that envelope to me it is a very easy decision to make.

I use a 50m zero for my fighting rifle and recommend it to others. I do not think your choice of optic should affect the zero chosen. The 50m would be my choice for iron's, a red dot or a scope. It's pretty awesome on my Burris MTAC. Really the only reason I can see going with another zero would be a gun with a concept of use other than a fighting rifle. For a DM or varmit gun I might look at a 36 meter zero to keep it within 4" out to about 350 meters.

The way I personally execute a 50 meter zero is to just do a 25 meter zero then back out to 50 and adjust the point of impact down to be on at 50m. The reason I do this is that it's a lot easier to get onto paper at 25m saving ammo then back it out to 50m. I think it's faster and certainly saves ammo by starting closer to zero (due to distance). Suppose I could move the sights sufficiently then confirm but I've been lazy and redneck adjusted (fire a group, move the sights, repeat as needed till on target).

Anyway that is why my rifle is zeroed at 50 meters and I suggest you do the same. That is my thinking on that.

[Jet Jaguar]

Bump

[null and void]

What is it that prevents someone from using the same scale when trying to illustrate a point?

Because the top scale is 10 times taller than the bottom scale the improved sighting looks worse at first glance!

[B4Ranch]

[Ruy Dias de Bivar]

I have somewhere a clipping from a hunting magazine showing how to sight in rifles at 25 yards and how it will react down range.

[Little Pig]

Doesn’t really make sense to me. The cartridge is the same, so why would it not rise the same amount over the same distance? Total bullet rise over 175 meters is 12 inches in the first graph. That should stay the same no matter where your zero is. There can’t be another 10” of drop from 0-12 meters on that second graph, can there? And why is the rise so much steeper in the second graph anyway? The curve should stay the same.

[Little Pig]

Should have added: if anything, the curve in the second graph should be shallower, since the horizontal scale is longer.

[Little Pig]

From what I understand, even with a level barrel, the .223 round does have a bit of rise; something to do with the spin of the bullet.

[LibWhacker]

I guess people just like to fill up the entire graphical area from top to bottom and from left to right, so you can see the curve better. But I’m with you, unless keeping both scales the same obscures the behavior of one of them, I say keep the scales the same!

[LibWhacker]

Correct! It’s no wonder anyone who thinks differently can’t hit the broad side of a barn!

[LibWhacker]

If you are zeroed at 1000 yards, say (just to look at an extreme case), your sights will cause you to shoot at a much greater angle, so you can hit the target out at 1000 yards. But this is also true at all distances at which you engage a target, causing you to miss high (if you don’t compensate by fiddling with your elevation and windage). So I guess that’s what the troops were doing... Just shooting without bothering to compensate for the distance.

[Oztrich Boy]

The curve should stay the same.

The curve is the same.

First principle. There is no such thing as bullet "rise". From the instant the bullet leaves the muzzle, it is dropping wrt the barrel bore line.

The sight line is aimed below the bore line to intersect the buller trajectory. At 25m the sight line cuts the trajectory early (and again c300m) to take a big "slice" out of the trajectory, consequently difference between curve and straight line is large.

At 50m (and c200m), the slice is smaller, shallower, consquently narrower, and the sight line is always closer to the trajectory

[oldenuff2no]

Exactly right.
I'm a gun smith and I didn't even follow what this guy was saying. When I'm putting a scope on a rifle I usually start somewhere between 7 and 10 yards and I'm looking for two things. First putting it dead on in the center of the X and second to fire a short string to see if they will stay there. If the bullets are hitting in a pattern that tells me the rifle is having a bedding problem, or the rings aren't tight or a few other things.
I save steps and ammo. After I have everything like I want it there I step it on out to a hundred yards, run a snake through the tube and check MOA. If it is not shooting 3/8” clover liefs off of a good mechanical rest at a hundred yards then something is wrong. I build or customize rifles that are very accurate and nothing else will do.
If a rifle is shooting a heavier bullet and not a “flat shooter” I start at 7 yards. If a rifle shoots a flat shooting round I start it off at 10 yards. You would be surprised how close it will fall in at a hundred. Most of my rifles are made to shoot accurately out to 800 or a 1000 yards. I do not chamber them for the .223 round.
My personal varmint rifles are sighted in dead on at all ranges and are packing shepherd varmint scopes with the 9 inch circles. I shoot two calibers for varmints depending on the size of the intended target. 22-250 for ground squirrel sized critters and a 6MM rem for coyote sized varmints. I do have one AR set up for accuracy. It does better than other AR's but doesn't come up to the point of my 22-250 bolt action rifles. The lock up is not as consistent and never will be and because of that the shot to shot accuracy will always be off a bit more.

[Stat-boy]

“That should stay the same no matter where your zero.”

Imagine a rifle with a scope, and the center of the scope is exactly 2 inches above the center of the barrel. If both the scope and the barrel are perfectly horizontal, if I aim through the scope at a target x at 10 yards, the bullet will strike 2 inches below the x. If I aim through the scope a target x at 50 yards, the bullet will strike about 2.01 inches below the x.

Does that help explain? When a rifle is zeroed in at a certain distance, meaning that we adjust the scope until the bullet hits the center of the x on the target, that means that the line of sight through the scope and that the aim of the barrel are not parallel to each other. In fact, one can draw three lines: (1) line from the center of the scope to the x on the target [this first line is the “sight line”]; (2) line from the x on the target to the center of the barrel; and (3) line from the center of the barrel to the center of the scope. these three lines from a triangle, with two very long sides and one very short side. In fact, assume a 50 yard zero, the two long lines are 50 yards and the short line is 2 inches.

Therefore, while firing a rifle with a scope, assuming that the rifle is zeroed in at some reasonable distance, if the sight line is perfectly horizontal, the barrel will be pointed slightly up from due horizontal.

The difference in the two ballistic graphs (one with a 25 yard zero and a second with a 50 yard zero) is that with the 25 yard zero the barrel is pointed higher.

P.S. I intentionally did not use metric measurements. Sorry, still rebelling from being told during elementary school that the US would go to the metric system-—ha!

[The Cajun]

Bookmark for later.

[Windflier]

Why does everything have to be in metric these days? I’m an American, and I like our traditional English measurements.

I know, I know. Base ten makes more sense, but dammit, I wasn’t raised on that system and can’t re-adjust overnight.

[doorgunner69]

All well and good for mouse gun cartridges....

A modest ballistics program, a bit of info on your cartridge and rifle, and you can make up your own zero range according to your estimated needs.

For iron sights and 7.62mm ammo, I still believe in the good old Marine Corps 300 yard battle sight. For scope use, 100 yards and knowledge of the drop at range work just fine. A 22-250 would be quite different were I to have one.

I had to laugh at some episode of Discovery or something showing a "secret" sniper method of shooting through a hole in a close-in screen that would mask the shooter. It was obvious they were shooting through the first zero and using the screen to mask the shot. Some secret.

Of course, ballistics geeks know all about the first zero crossing happening well before the long range crossing and the ability to do a prelim sighting in at that close range first. Firing at the real zero range almost always seems to be a touch off, but that is the fun of shooting after all.

[LibWhacker]

I’m with you! We don’t need metric. We’ve never needed it. In fact, I maintain that if you need a simplistic intellectual crutch, like the metric system, you should go into art and poetry and leave the sciences, engineering and the actual building of things to people with a head on their shoulders!

[NonValueAdded]

Wow! That’s the “Ah, I get it now” graphic.

[The Cajun]

but dammit, I wasn’t raised on that system and can’t re-adjust overnight.

Right you are!
I hate metric with a passion.
Traditional measurement are just second nature, requires no thinking hardly.
Give me something in metric and I have to go through mental gymnastics to picture some distance that used to be automatic.

Don't get me started on stinking metric bolts and metric tools.