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Old February 20, 2012, 07:55 PM   #1
MyCleverSN
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Zeroing a rifle question..

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.
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Old February 20, 2012, 08:14 PM   #2
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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.
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Old February 20, 2012, 08:15 PM   #3
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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.
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Old February 20, 2012, 08:32 PM   #4
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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...
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Old February 20, 2012, 08:32 PM   #5
MyCleverSN
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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.
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Old February 20, 2012, 08:34 PM   #6
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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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Old February 20, 2012, 08:39 PM   #7
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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!!
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Old February 20, 2012, 08:39 PM   #8
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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.
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Old February 20, 2012, 08:41 PM   #9
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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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Old February 20, 2012, 08:43 PM   #10
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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...)
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Old February 20, 2012, 08:44 PM   #11
MyCleverSN
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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.
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Old February 20, 2012, 08:46 PM   #12
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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.
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Old February 21, 2012, 03:37 PM   #13
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Basic .223 calculator
1.5" high optic
25 yard zero








100 yard zero
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Old February 21, 2012, 04:59 PM   #14
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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.
IME, 125/150m is what units in the Army use for standard military loads (for the units that confirm a second zero at range).
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Old February 21, 2012, 05:23 PM   #15
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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.
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Old February 21, 2012, 06:11 PM   #16
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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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Last edited by moxie; February 21, 2012 at 06:22 PM.
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Old February 21, 2012, 06:22 PM   #17
AK103K
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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.
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Old February 21, 2012, 08:03 PM   #18
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Old February 21, 2012, 09:29 PM   #19
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You still have to confirm that your zero is correct for the longer distances.
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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Old February 21, 2012, 09:49 PM   #20
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Old February 21, 2012, 10:19 PM   #21
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I don't get the practicality of a 25 yard zero...
It imposes a rather steep muzzle angle, making the round far more inaccurate at closer ranges than it need be. According to the chart above, nearly 4" high at 150- where's the advantage in that?


Quote:
Dont plan on 800m with a mosin unless your just playing around.
I can bang 8" steel at 600 yards with my Mosin sporter. You don't know what you're talking about. The ballistics of the 7.62 x 54R are quite capable of long range- right up there with the 30.06.

Go bone up on your ballistics tables...
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Old February 22, 2012, 12:39 AM   #22
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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...
The Gunny got it right, as did some others. The bullet crosses the line of sight twice. Zeroing at the closer range puts the bullet back on target at the longer range, with the bullet being high at midrange. For the hunter, zero as far out as possible without being too high in between.

You can zero all rifles for the same closer range, but, as mentioned, the velocity and load determine where it crosses the line of sight the second time (zeroes).

Battle sight zero is about 250 or maybe it's 300 meters. The idea is to put the sights on the enemy's mid section and hit him somewhere.

For many of us in the urban environment, a 100 yds. zero is fine. Remember our rules of engagement are different. Better have a good, court defensible reason for shooting someone at distance.
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Old February 22, 2012, 12:59 AM   #23
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This is where my question comes in for the M4 as well as a sniper rifle that I am building.
You are building a sniper rifle while you are still struggling with basic ballistics? My, you are an ambitious fellow. I'm sure you'll get it all down soon.

The base reason is gravity. The bullet starts dropping as soon as it leaves the muzzle. And its moving "sideways" pretty fast,as it falls.

To compensate for this (as much as we can) gun barrels are "pointed up", compared to the line of sight, which is straight at the target. Although they look parallel to the eye, the line of the bore and the line of sight are not. So the bullet is fired "up", and crosses the line of sight going up a short distance from the muzzle.

Then as it flies downrange, falling, it crosses the line of sight again, on its way down. The distance from the muzzle where this happens is where your sights and bore are "zeroed". Adjusting the sights allow us to decide at what range that second crossing happens, 100, 200, 300yds, etc.

Velocity and bullet construction determine the arc of the trajectory. For the M16A1 using the GI ball ammo of the 1970s (which I have personal experince with), hitting a certain spot on the 25 meter target meant that you would hit the desired spot at 250 meters.

This principle will work for all rounds, and to zero at any chosen distance, all that needs to be done is calculate the right spot on the 25 meter target. It will be different for different guns and loads.
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Old February 22, 2012, 07:46 AM   #24
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"Sniper rifle" = a weapon used to kill 2 legged prey.

The term is used pretty loosely around here...just call it a "precision" or "tactical" rifle...
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Old February 22, 2012, 08:57 PM   #25
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It imposes a rather steep muzzle angle, making the round far more inaccurate at closer ranges than it need be. According to the chart above, nearly 4" high at 150- where's the advantage in that?
I am thinking that if I am aiming for COM chest and I hit 4" high that ain't all bad.

Quote:
"Sniper rifle" = a weapon used to kill 2 legged prey.
He might not be talking about kangaroo. He might be talking about snipe.
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