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Posted: 3/8/2014 9:38:25 AM EDT
| I have a Bushmaster xm15 e2s that I just topped off with a nikon p-223 4x12 scope. Problem I am having is at 25 yards I am a inch high at 50 yards I am 5 inches high and at 75 I am 9 high. Why is the bullet climbing? Couple quick googles say this is common with AR platform rifles. Anyone else have this happen? I can't see how the bullet is climbing 9 inches in 50 yards. Any help or suggestings will be a big help. Tomorrow I am going to just sight it in at 100 and see what happens from there. Shooting 55gr soft points |
| the height of the mounts, bullets you are shooting and are you shooting prone or from a bench or standing. if you think about it line of sight from the scope will make sense. if you plan on 100 yrds then zero at that range and be done with it. its all about angles between the scope and bore. |
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I have a Bushmaster xm15 e2s that I just topped off with a nikon p-223 4x12 scope. Problem I am having is at 25 yards I am a inch high at 50 yards I am 5 inches high and at 75 I am 9 high. Why is the bullet climbing? Couple quick googles say this is common with AR platform rifles. Anyone else have this happen? I can't see how the bullet is climbing 9 inches in 50 yards. Any help or suggestings will be a big help. Tomorrow I am going to just sight it in at 100 and see what happens from there. Shooting 55gr soft points It's common with all firearms. It is caused by the fact that your sights are a certain distance above your bore. When the bullet exits the bore, it's below your line of sight so you adjust your sight so that the bore and the sights are at an angle to each other. In effect, you are actually tilting the barrel up in relation to the sight line. Additionally, the bullet begins to drop succumb to the effects of gravity immediately upon exiting the muzzle. due to gravity. The AR has sights that are pretty high above the bore, creating a pretty severe sight to bore angle. It's much more noticeable than, say, a 30-30 lever gun with a bead front sight sitting right on the barrel. There is still an angle, but not nearly as much as a typical AR. Try using a ballistics calculator to determine where you want your bullet impact to be. Here's a decent one and there are many others out there. Use the advanced options to play around with the sight over bore distance to get a better grasp of what we're talking about. Ballistics Calculator 
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Quoted:
It's common with all firearms. It is caused by the fact that your sights are a certain distance above your bore. When the bullet exits the bore, it's below your line of sight so you adjust your sight so that the bore and the sights are at an angle to each other. In effect, you are actually tilting the barrel up in relation to the sight line. Additionally, the bullet begins to drop succumb to the effects of gravity immediately upon exiting the muzzle. due to gravity. The AR has sights that are pretty high above the bore, creating a pretty severe sight to bore angle. It's much more noticeable than, say, a 30-30 lever gun with a bead front sight sitting right on the barrel. There is still an angle, but not nearly as much as a typical AR. Try using a ballistics calculator to determine where you want your bullet impact to be. Here's a decent one and there are many others out there. Use the advanced options to play around with the sight over bore distance to get a better grasp of what we're talking about. Ballistics Calculator http://upload.wikimedia.org/wikipedia/en/a/a8/TargetShooting3.gif (edited for more accurate description) Quoted:
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I have a Bushmaster xm15 e2s that I just topped off with a nikon p-223 4x12 scope. Problem I am having is at 25 yards I am a inch high at 50 yards I am 5 inches high and at 75 I am 9 high. Why is the bullet climbing? Couple quick googles say this is common with AR platform rifles. Anyone else have this happen? I can't see how the bullet is climbing 9 inches in 50 yards. Any help or suggestings will be a big help. Tomorrow I am going to just sight it in at 100 and see what happens from there. Shooting 55gr soft points It's common with all firearms. It is caused by the fact that your sights are a certain distance above your bore. When the bullet exits the bore, it's below your line of sight so you adjust your sight so that the bore and the sights are at an angle to each other. In effect, you are actually tilting the barrel up in relation to the sight line. Additionally, the bullet begins to drop succumb to the effects of gravity immediately upon exiting the muzzle. due to gravity. The AR has sights that are pretty high above the bore, creating a pretty severe sight to bore angle. It's much more noticeable than, say, a 30-30 lever gun with a bead front sight sitting right on the barrel. There is still an angle, but not nearly as much as a typical AR. Try using a ballistics calculator to determine where you want your bullet impact to be. Here's a decent one and there are many others out there. Use the advanced options to play around with the sight over bore distance to get a better grasp of what we're talking about. Ballistics Calculator http://upload.wikimedia.org/wikipedia/en/a/a8/TargetShooting3.gif (edited for more accurate description) I understand what your saying but how can that be fixed besides just knowing the ballistics of your bullet? |
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Excellent reply by crcristo, because of the design this effect is exaggerated w/ the AR platform. As suggested, w/ tools like a
ballistics calculator, a chronograph or simply range time you can compensate for this effect but you can't really "fix" it because it's not broken. |
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Sight it in for the distance you're most likely to be shooting at. From there, you have to learn hold-overs (-unders). As has already been said, usually a 100 yard zero works best for people.
Check out this article for more in-depth discussion: http://www.shootingillustrated.com/mobile/article.php?id=23123 |
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Quoted:
I understand what your saying but how can that be fixed besides just knowing the ballistics of your bullet? Quoted:
Quoted:
Quoted:
I have a Bushmaster xm15 e2s that I just topped off with a nikon p-223 4x12 scope. Problem I am having is at 25 yards I am a inch high at 50 yards I am 5 inches high and at 75 I am 9 high. Why is the bullet climbing? Couple quick googles say this is common with AR platform rifles. Anyone else have this happen? I can't see how the bullet is climbing 9 inches in 50 yards. Any help or suggestings will be a big help. Tomorrow I am going to just sight it in at 100 and see what happens from there. Shooting 55gr soft points It's common with all firearms. It is caused by the fact that your sights are a certain distance above your bore. When the bullet exits the bore, it's below your line of sight so you adjust your sight so that the bore and the sights are at an angle to each other. In effect, you are actually tilting the barrel up in relation to the sight line. Additionally, the bullet begins to drop succumb to the effects of gravity immediately upon exiting the muzzle. due to gravity. The AR has sights that are pretty high above the bore, creating a pretty severe sight to bore angle. It's much more noticeable than, say, a 30-30 lever gun with a bead front sight sitting right on the barrel. There is still an angle, but not nearly as much as a typical AR. Try using a ballistics calculator to determine where you want your bullet impact to be. Here's a decent one and there are many others out there. Use the advanced options to play around with the sight over bore distance to get a better grasp of what we're talking about. Ballistics Calculator http://upload.wikimedia.org/wikipedia/en/a/a8/TargetShooting3.gif (edited for more accurate description) I understand what your saying but how can that be fixed besides just knowing the ballistics of your bullet? One of us isn't understanding the other, I think. If I'm understand what you're saying correctly, there isn't anything to fix. For the sights/scope to work, the muzzle must be angled up as related to your sight line. If it isn't, your round will never cross the path of your sight line. I pasted the results of a ballistics calculator below. I could have played around with it a bit more to get it even closer to what you described. I don't know your sight height over bore, or what your velocity is, among other factors. Still these numbers are pretty close to what you are describing. They indicate that you are zeroed at about 12 yards. In other words, if you put a target out at about 12 yards, you're going to be pretty much hitting exactly what you're aiming at. That's fine, if that's really what you want, (you shouldn't, but it's yours) but in order for the bullet to intersect your sight line at 12 yards, it has to climb the distance between your muzzle and your reticule in the first 12 yards of travel. That's a pretty extreme angle, and it will keep climbing for the next 250 yards before it starts to fall back to earth. If you want to get real close to a 100 yard zero, you should probably be adjusting your sights to hit somewhere between .75" - 1" below your point of aim at 25 yards, not 1" high. Bullet Weight: 55 gr Altitude: 0 feet Ballistic Coeffcient: 0.222 Max Range: 200 yd Muzzle Velocity: 3240 fps Test Barrel: 24 in Sight Height: 1.5 in Range (yd) Drop (in) Wind Drift (in) Velocity (FPS) Energy (ft/lb) 0 -1.5 0.0 3240 1282 5 -0.9 0.0 3217 1264 10 -0.2 0.0 3194 1246 15 0.4 0.0 3171 1228 20 1.0 0.1 3148 1210 25 1.6 0.1 3126 1193 50 4.4 0.3 3014 1109 75 7.0 0.7 2906 1031 85 8.0 0.9 2863 1001 95 8.9 1.1 2821 972 100 9.4 1.2 2800 957 |
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