Zeroing a rifle question..

M

MyCleverSN

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Okay so I guess you can say I'm quite new to guns. I've grown up liking them as a little boy and joined the Army national guard(11b) 2 years ago and went to OSUT at Ft Benning. That was the first time I ever shot a gun..

The only rifle I have ever zeroed is the standard issue M4 carbine in OSUT and drills when we go to the range(Which is practically never, it's bs, infantry unit that never shoot... how bout that). We zero I believe at 25M for a 300M range. This is where my question comes in for the M4 as well as a sniper rifle that I am building. How does zeroing at 25M make the weapon zeroed effectively at 300M? Does this mean if I zero at a further distance than 25M then the weapon is zeroed for further targets? Or is there a set limit on where to zero and that weapon is zeroed with your sights/optics and you adjust appropriately to wind direction, height, wind speed ect...?

I'm building a cheap sniper rifle for no more then $300. If I zero this rifle at a indoor shooting range to my "scope" at 25 YARDS, how far is it zeroed to?

THANKS
I'm building the sniper rifle out of a Mosin Nagant 9130.
 
Alright, rough answer since I do not know your velocity, bullet, etc.

BUT zeroed at 25 yards your should be about an inch high at 50, 2.5 inches high at 100, just about zeroed at 200, and about 9 inches low at 300.

Again, just a ballpark, but i bet it would be fairly close.
 
If you would like to learn more about firearm ballistics I would recommend "Understanding Firearms Ballistics" by Robert A. Rinker.
It's is a very good read and covers basic to advanced ballistics in a manner that makes it easy to understand whatever your experience level.
 
When a bullet is fired it typically meets your line of sight twice, once on the way up and again on the way down to meet your zero, much like throwing a rock - more distance untill target = higher trajectory needed untill it comes down to hit target. The faster your bullet and higher your ballistic coificent is the less noticeable this is. What they (Army) probably did is zeroed at 300 then moved in untill it was on zero again. If you tell me what ammo your using and what range you want your rife zeroed I can give you the first point of intersecion...
 
So basically you need to zero the rifle at around 100M for it to be effective 800M+? Thanks for the book name, I'll DL it.
 
Don't they give out SMART manuals anymore?

Look at your SMART manual and it explains why you zero your weapon at 25 meters.

The trajectory of the bullet breaks the line of sight on it's way up at 25m, it breaks the LOS on it's way down (as it's falling) right around 300m, or at least it's suppossed to.

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So basically you need to zero the rifle at around 100M for it to be effective 800M+? Thanks for the book name, I'll DL it.

No, No never never!!
 
Of course I don't know your load or ammo, but based on what I shoot out of my Mosin, (174 grn @ 2450 FPS), if you zero at 25 yards you're going to be 2 inche high at 100 yards, about 3/4 in low at 200 and 4.5 inches low at 300.

Lets say you sight in 2 inches high at 25 yards. That would put you at 2.75 high at 100, right on at 200 (range used by the Mosin in CMP GSM matches), and 3.75 inches low at 300.

The 200 yard zero would cover you in any normal hunting ranges people shoot.

You can sight in at 2 inchs high at 25 to get close to a 200 yard zero, but I'd highly recommend finding a 200 yard range and confirm your zero.
 
The 25m zero is just a rough zero, you still need to confirm the zero at the different distances and fine tune it. It may (or may not) be close, and its not likely going to be perfect.
 
Dont plan on 800m with a mosin unless your just playing around. Dont get me wrong, I like them but not a 800m gun. Take a paper plate and try different distances untill you miss, that is your max range for deer sized game (Deer, people, zombies...)
 
I understand that bullets drop because of gravity and you need to adjust for this (I shot higher on the 500M targets at camp pendleton and hit them dead on).

I just assumed that since I plan on shooting 600M+ targets with this 9130 that I would zero farther then 25M. I appreciate the help fellas, thanks. I'm going to research more. I've always been intrigued at the thought of being able to hit 1000M targets with such accuracy. I don't now much about guns right now, but I shoot pretty damn good(As far as the military weapons. M249, M240B, M4, M16) I don't think I'll ever go through sniper school with the Army, but I will train on my own.
 
It's not as confusing as it seems at first. Read this slowly.

Because of gravity the bullet starts to fall as soon as it leaves the barrel. To compensate for that, the sights are adjusted so the bullet will go up and cross the line of sight (through the sights) at 25m in this case. (The bullet leaves the barrel below the line of sight because the sights are atop the barrel.)

As gravity continues to work, the bullet falls more, making an arc from the muzzle to the ground. On it's way to the ground, therefore, it passes through the line of sight again. This of course is further down range. In between the two points of passing through the line of sight the bullet will be above the line of sight.

It's common to sight in at a shorter range for longer range, then check the longer range for fine tuning of the sighting in.

It's interesting to note that the laws of physics make the bullet drop at the same rate as another similar object. So if you had a bullet in your hand and dropped it at the instant you fired your rifle while it's level, both bullets would hit the ground at the same time.

That's a simple explanation. Do some studying. You'll learn there are charts and computer programs that will solve the ballistics of most every bullet made. You'll find it very interesting once you get into it.
 
The 25m zero is just a rough zero, you still need to confirm the zero at the different distances and fine tune it. It may (or may not) be close, and its not likely going to be perfect.
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IME, 125/150m is what units in the Army use for standard military loads (for the units that confirm a second zero at range).
 
If the army is zeroing at 25m and not comfirming and practicing regularly at the other distances, perhaps thats why the 5.56 gets such a bad rap as a stopper. ;)
 
The military has always zeroed the M-16 and its variants at 25 meters. Once zeroed at 25M you're good to go at 300. For 200 and less you use the larger aperture peep and over 200 you flip to the smaller aperture peep sight and change the elevation wheel to the appropriate setting. This assumes use of standard 193/855 ammo which are nearly identical in terms of trajectory. Heavier or different types of bullets driven at different velocites have different trajectories.

Tables and computer programs are available that show trajectories for any combination of caliber/bullet/ballistic coefficient/velocity. You need to know what your setup does. For example, many hunters zero their rifles at 25 or even 100 yards. They know the bullet rise or drop at various distances shorter than or farther than that 25 or 100 yards and hold over or under to compensate. Many scopes have reticle marks that allow the shooter to easily adjust his hold. All of this is called exterior ballistics and can be a lot of fun. There are plenty of resources available on the net and elsewhere.
 
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You still have to confirm that your zero is correct for the longer distances. In order for your 300 yard zero to be correct, requires your 25 yard zero to be "perfect". Of course, all of this is just "mechanical", and things like wind, and other factors are not being considered.

Even with all the ballistic tables and computer programs, you still need to physically confirm that that load out of your rifle does in fact do what it says on paper. They may be close, and often they are not. The only way to really know, is shoot the gun and confirm it.
 
You still have to confirm that your zero is correct for the longer distances.
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Most units confirm this by shooting targets out to 300m at the qualification range. Some units go the extra mile and conduct a confirmation range. Some (poor) units fire ALT-C which is the miniature silhouettes at 25m. The last is really bad policy and normally only done by certain support units, National Guard and really poorly run other units.
 
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