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Posted: 6/25/2001 7:27:47 PM EDT
OK, I aded a 3-9x42 scope to my AR15, A1 upper, and I sighted in in at the local indoor range, which is only 25 yards. I know that one of the newer zero'ing methods is the 50/200 yard method, where you zero at 50 yards instead of meters, and that puts you dead on at 200 yards, and 2" low at 250 yards. At 25 yards, off a bench, I was getting 5 shot groups about .35" groups, not center to center, but edge to edge at the widest point. The group was 3/8" above point of aim, at 25 yards. How do I calculate where it would be at 50 yards, so that I can dial it in? It is 1/4/MOA clicks, so 4 clicks would be 1" at 100 yards, meaning that 4 clicks at 25 yards would be .25", do I have this right? Now, where SHOULD it be hitting at 25 yards, to be zero'd at 50 yards, and am I correct in assuming that I can just dial it in according to what you tell me, and I should be within a click or two at 50/200 yards? I read some of the recommended methods on some of the AR15 info pages posted throughout this forum, but there are several different methods, and I am not sure which one I matches what I am trying to do. Help! please. ;-)
Link Posted: 6/25/2001 8:39:05 PM EDT
[Last Edit: 6/25/2001 9:00:20 PM EDT by SquireSCA]
Not one person knows? 30 people have read this so far and not one person can chime in with a simple, "5/8" low" or whatever? hehehe Come on guys, help a brutha out!
Link Posted: 6/25/2001 9:42:46 PM EDT
For the love of Pete... The most knowledgeable and heavily visited source of AR15 knowledge in the wrold, and not a single person will post an answer to what should be a simple question... I am gonna go ask my cat, maybe he knows...
Link Posted: 6/25/2001 9:45:42 PM EDT
Sorry S. I keep looking every time I see a new post here to get that info myself. Aviator [img]www.dredgeearthfirst.com/aviator.gif[/img]
Link Posted: 6/25/2001 9:52:22 PM EDT
Link Posted: 6/26/2001 5:32:43 AM EDT
Finally some answers! hahaha Not an exact answer yet, but we are getting somewhere... I kept lokking around the net, and one page said that to set your zero to 20 meters, to move it down(I assume) 3/8" from normal, which I am also assuming is a 50/200 zero. So I moved my scope down 7 clicks. But again, this is all guesswork, I am not sure, as there are so many methods, some in meters, some in yards, etc... Hopefully someone will stumble in here with an exact number...
Link Posted: 6/26/2001 5:41:08 AM EDT
Here are 5 methods [url]http://communities.msn.com/TheMarylandAR15ShootersSite&naventryid=120[/url]
Link Posted: 6/26/2001 5:44:50 AM EDT
I read the Maryland site, but I could not find the information I was looking for. I simply wish to know, that if I am going to use the 50/200 yard zero, how low would I be hitting at 25 yards? 1/2"? 3/8"? Is there even a difference from 25 to 50 yards?
Link Posted: 6/26/2001 5:47:56 AM EDT
You want an exact number from someone, but there are so many variables unknown that no one who knows what they're doing would be able to give you that information. What's your load's velocity? The ballistic coefficient of your bullet? Distance bore to line of sight? Barrel rise during bullet transit? Temperature? Humidity? And I could rattle off a dozen more. Yes, those are all small factors, but remember, you want an exact number. If you're on paper at 25 you'll be on paper at 200. If you shoot 200 you'll get your zero then. If you don't, it doesn't matter.
Link Posted: 6/26/2001 5:50:48 AM EDT
[Last Edit: 6/26/2001 5:51:10 AM EDT by ECS]
[url]communities.msn.com/TheMarylandAR15ShootersSite&naventryid=153[/url] This covers the 25 Yard method. If your rifle is zeroed at 300 yards then your bullet is rising at 25. Your bullet starts out below line of sight, rises above line of sight, and then fall exactly to line of sight at 300 yards, if thats what you are zeroed at. 25 yards is a very short distance for a rifle zero. I would rezero at a longer distance whenever you do get the chance to.
Link Posted: 6/26/2001 6:19:40 AM EDT
OK, I realize that I cannot expect an EXACT measurement... hehe But 25 yards is the limit of the indoor range. That was what I have to work with at this point. So if I wanted to be zero'd at 50/200 yards, I am guessing that I want to be hitting 1/4" or 3/8" low at 25 yards, as the bullet is still on the rise. Is that approximately correct?
Link Posted: 6/26/2001 6:37:33 AM EDT
Originally Posted By SquireSCA: OK, I realize that I cannot expect an EXACT measurement... hehe But 25 yards is the limit of the indoor range. That was what I have to work with at this point. So if I wanted to be zero'd at 50/200 yards, I am guessing that I want to be hitting 1/4" or 3/8" low at 25 yards, as the bullet is still on the rise. Is that approximately correct?
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The referenced article says to set your rear sight to 400 meters, plus 2 clicks, then zero at 25 yards adjusting the front sight. After that the rear dial should be approx. correct at the indicated distances.
Link Posted: 6/26/2001 6:46:09 AM EDT
Be careful about 'clicks' on A2 or is it A3 uppers. One of mine clicks 4 times between the #'s. ie 4 clicks from 200 to 300. The other A3 of mine is actually in half clicks. So it takes 8 clicks to go from 200 to 300. Make sure you know how yours works when you follow destructions. [;)]
Link Posted: 6/26/2001 6:56:29 AM EDT
Originally Posted By ECS: Your bullet starts out below line of sight, rises above line of sight, and then fall exactly to line of sight at 300 yards,
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Is this bullet on auto pilot? The bullet will start to drop the very instant it leaves the barrel. Gravity affects all objects equally. The rise and drop is only percieved due to the sights being above the barrel.
Link Posted: 6/26/2001 7:03:51 AM EDT
My range has targets at 20 yards and 33 yards, which should I put my zeroing targets at and what corrections should I made to the windage and elevation for a 25 meter zero? Kharn
Link Posted: 6/26/2001 7:06:59 AM EDT
Remember, that I am using a SCOPE, my iron sights are not the issue. I don't even need to know how many clicks, just need to know that if I want to be zero'd at 50 yards with a 16" carbine, how low(approximately) should I be hitting at 25 yards. You give me the measurement, and I will figure out the clicks... ;-)
Link Posted: 6/26/2001 8:10:33 AM EDT
Originally Posted By RipMeyer:
Originally Posted By ECS: Your bullet starts out below line of sight, rises above line of sight, and then fall exactly to line of sight at 300 yards,
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Is this bullet on auto pilot? The bullet will start to drop the very instant it leaves the barrel. Gravity affects all objects equally. The rise and drop is only percieved due to the sights being above the barrel.
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Assuming you are sighting at a level target, the bullet flies the same type trajectory as a football does. The quarterback has to throw it in an upward arc initially, so that by the time the football has traveled to the receiver it has risen, then fallen back to the receiver. Its the same story with bullets, only they don't rise and fall quite as much. Your barrel initially will be pointing up slightly, to hit a level target. Gotta happen.
Link Posted: 6/26/2001 8:15:53 AM EDT
Originally Posted By SquireSCA: Remember, that I am using a SCOPE, my iron sights are not the issue. I don't even need to know how many clicks, just need to know that if I want to be zero'd at 50 yards with a 16" carbine, how low(approximately) should I be hitting at 25 yards. You give me the measurement, and I will figure out the clicks... ;-)
View Quote
Can't do it - all the figures you see quoted for sighting in at different distances are for iron sights, which are a know distance from the bore line. Don't know how high your scope is from the bore. I would simply scope dead on at 25. Then, later if you ever shoot it at a greater distance you can adjust for some longer distance. Whats wrong with that?
Link Posted: 6/26/2001 9:16:15 AM EDT
Hi I've been reading along for a while, but had to become a member for this one, as it seemed to be such an interesting question. Here goes a shot at it: The simple answer is: measure the distance between your bore and your scope and divide it in half. This is the amount you should be low at 25 yards for a 50 yard zero. There are many other factors which play in to this, but at this range and .223 velocities they are neglegible. However, they do form an interesting problem for some quick calculations. The way to visualize ballistics is that you have some sort of sight above your muzzle. The line of sight is ALWAYS a straight line as it is not affected by gravity. The bullet will follow a trajectory as was mentioned earlier. Essentially sighting in is moving your line of sight until is interesects the trajectory. It will do this in two places- once with bullet going up, and once as it goes down. For easiers visualization, picture the line of sight being horizontal, and the barrel being angled up to provide the trajectory. If you look at it this way, and say your scope is 2 inches above the muzzle, and you want the bullet to impact on line of sight at 50 yards, it must be half way there at 25 yards, so it will be low 1/2 of the distance between the muzzle and the sight. This is an over simplification, as we will see below, but as shown below, the ignored variables are irrelavent at these distances.
Link Posted: 6/26/2001 9:29:13 AM EDT
The above post does not factor in the drop of the bullet as it travels. This drop is given by the formula D= 1/2 a t2. (distance of drop equals one half of the aceleration of gravity times the time of flight squared. The accereration of gravity is a constant- 32feet per second squared. Thus we need to know the time of flight to factor in the drop. For this we need the velocity and the ballistic coefficient of the bullet. Lets say you use a bullet with a BC of .34 at a velocity of 3200 fps. The best way to prove this is with a ballistics program, but I don't have one, so numbers are taken from the speer relading manual number 11. Given a bullet BC of .34 and velocity of 3200, at 100 yds. the velocity is down to 2906 a drop of 294 fps. Now this is where a ballistics table comes in handy, as a good one will calculate the velocity at every foot- instead I will interpolate velocities here which will give an approximation of bullet drop. Lets say that at 50 yards the velocity drop is 1/2 of that at 100yds, and the velocity drop at 25 yards is 1/4 of that at 100 yards. This is not entirely true as the velocity drop is not linear (hence why programs calulate it at each foot). Making this assumption, the velocity at 25 yards is 3126.5 fps, and at 50 yds, it is 3053 fps.
Link Posted: 6/26/2001 9:54:19 AM EDT
Using the above information, we can approximate the average velocity of the bullet over the flight out to 25 and 50 yards. Again, since the drop in velocity is not linear, we are only approximating. The velocity starts at 3200 fps and is 3126.5fps at 25 yds. This gives an average of 3162.25 (3200 + 3126.5)/2. The average velocity out to 50 yards is 3126.5 fps. We now use these numbers to calculate the time of flight: for 25 yds: 75 feet / 3162.25 f/sec = .0237 sec for 50 yds: 150 f / 3126.5 f/sec = .0479 sec We can use this to calculate the bullet drop (1/2 at2 formula) Thus the bullet drop at 25 yds is: 1/2 x 32 f/sec/sec x .0237 squared = .00898 ft or .10 inches For 50 yds: 1/2 x 32 f/sec/sec x .0479 squared = .0367 ft or .44 inches. Therefore, the differece between the 25 and 50 yd drops is .34 inches, so at this bullet BC and velocity, you would have to add .34 inches to the number you obtained when you divided the distance between your muzzle and sight in half to find the amount the bullet must come up at 25 yards for a 50 yard zero ( i.e. if there is 2 inches between sight and barrel then 1" plus .34", which means you would be 2"-1.34" low at 25 yds, or .66". I guess this came out to be more significant than I thought. I think this is right, now if you get a chance to check it in reality, let me know. P.S. don't forget to refigure based on your BC and velocity.
Link Posted: 6/26/2001 10:05:45 AM EDT
Link Posted: 6/26/2001 12:01:53 PM EDT
BTW this is all a moot point, as I think the 50/200 method is dependent on the height of the iron sights above the bore, so it will not work with a scope on the carry handle. You will be significantly high at 200, as your climb to get to zero at 50 is significantly steeper.
Link Posted: 6/26/2001 12:58:31 PM EDT
This has been driving me nuts all morning. I think I made a mistake at the end up there. The drop is 0.44 inches at 50 yds, but only half of that has to be made up at 25 yds, so it could be that you should be 2" (height of sights) + 0.44 (amount of drop) all divided by 2 (half way to 50 yards when the bullet hits at 25 yards) minus 0.1 (drop at 25 yards) which would be 0.78 inches low at 25 yards. But, the more I think, the worse it gets. I guess that's why God made ballistics calculators.
Link Posted: 6/26/2001 1:02:59 PM EDT
Damn... I had no idea it was this complicated... hahaha OK, I will simply sight it in at 100 yards, so that it hits 1" high, which should put me at roughly centered at 200 yards, correct?
Link Posted: 6/26/2001 1:04:51 PM EDT
Let's make this easy. WHERE CAN I DOWNLOAD A BALLISTIC CALCULATOR? hehe
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