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Posted: 1/11/2009 4:41:30 PM EDT
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I developed a mid range load for practice, and went to the range to zero one of my rifles.
Zero at 50 yards with the load used was hitting at dead center of target. I then went to the hundred yard range to verify, expecting the round to print about 1-1.5 inches high, but found the round hitting about 2.5-3 inches high... much higher than expected... Here is the specs on rifle, sight, and round... 16" LMT upper 1/7", Aimpoint M2 with Larue Mount on a KAC RAS II rail. The load was 24 grains of 2230 behind a hornady 55 FMJ with CCI 400 primers, LC brass trimmed to 1.75", 2.25" OAL... not sure what velocity was, I don't currently have a chronograph. Is there something I am missing or does this seem abnormal? I was expecting this to be much closer to 1" high at 100 than 2.5-3"... just trying to get an idea of where to start to correct this. Thanks! Dave |
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I developed a mid range load for practice, and went to the range to zero one of my rifles. Zero at 50 yards with the load used was hitting at dead center of target. I then went to the hundred yard range to verify, expecting the round to print about 1-1.5 inches high, but found the round hitting about 2.5-3 inches high... much higher than expected... Here is the specs on rifle, sight, and round... 16" LMT upper 1/7", Aimpoint M2 with Larue Mount on a KAC RAS II rail. The load was 24 grains of 2230 behind a hornady 55 FMJ with CCI 400 primers, LC brass trimmed to 1.75", 2.25" OAL... not sure what velocity was, I don't currently have a chronograph. Is there something I am missing or does this seem abnormal? I was expecting this to be much closer to 1" high at 100 than 2.5-3"... just trying to get an idea of where to start to correct this. Thanks! Dave You need a chronograph. If your "mid-range" load is shooting significantly slower than "standard load" ammo, you'll need to dial in more elevation to zero at fifty yards. Because of this increased elevation at fifty yards, you're putting more of an "arc" on the bullets trajectory, which results in the higher point of impact at 100 yards. |
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There is nothing wrong with what you are doing. The 50 yard/200 yard zero will give you a + or - 2.5" trajectory out to about 225 yards. As the bullet rises past zero at 50 yards it will be approx. 2" at 100 yards rising to 2.5"-3" around 150 yards. You'll get a 4" drop at 250 yards and an 8" drop at 300 yards. There will some variance depending upon barrel length and muzzle velocity of the bullet. So your rounds impacting at 2.5" at 100 yards shouldn't be too much of a surprise. There is also the practical vs. theory so if you have time you should try placing a targets at 50, 100, 150, 200, 225, 250, 300 yards and see how your real results equate to theory (the ballistic calculator). They will probably be fairly close, but I am sure some variance by a few inches.
There is an article in the Oct 08 issue of SWAT magazine on the different BZO's that explains the why in detail. It is applicable to Red Dot Sights as well. http://www.swatmag.com/archive_2008/oct08.php S/F |
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Quoted:Is there something I am missing or does this seem abnormal? I was expecting this to be much closer to 1" high at 100 than 2.5-3"... just trying to get an idea of where to start to correct this.
Keep in mind that the higher your sights are above the bore, the higher your 100yd impact point will be from a 50yd zero. Also, you didn't mention how many rounds you used for your groups. If you shot 3-round groups at each distance then you could easily see an extra inch or so difference between the two centers just because of random variance. Ten round groups are better for verifying zeros. |
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I developed a mid range load for practice . . . You need a chronograph. If your "mid-range" load is shooting significantly slower than "standard load" ammo, you'll need to dial in more elevation to zero at fifty yards. Because of this increased elevation at fifty yards, you're putting more of an "arc" on the bullets trajectory, which results in the higher point of impact at 100 yards. Nonsense. 
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Quoted:Is there something I am missing or does this seem abnormal? I was expecting this to be much closer to 1" high at 100 than 2.5-3"... just trying to get an idea of where to start to correct this.
Keep in mind that the higher your sights are above the bore, the higher your 100yd impact point will be from a 50yd zero. Also, you didn't mention how many rounds you used for your groups. If you shot 3-round groups at each distance then you could easily see an extra inch or so difference between the two centers just because of random variance. Ten round groups are better for verifying zeros. Buck_Naked, pay attention to this man, for he knows of what he speaks. |
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Quoted:Is there something I am missing or does this seem abnormal? I was expecting this to be much closer to 1" high at 100 than 2.5-3"... just trying to get an idea of where to start to correct this.
Keep in mind that the higher your sights are above the bore, the higher your 100yd impact point will be from a 50yd zero. Also, you didn't mention how many rounds you used for your groups. If you shot 3-round groups at each distance then you could easily see an extra inch or so difference between the two centers just because of random variance. Ten round groups are better for verifying zeros. Buck_Naked, pay attention to this man, for he knows of what he speaks. So if I am running an Aimpoint that co-witnesses the sights in the lower third, that height over bore would be added to the approximate 1.5" trajectory that the chart shows? Whats the difference between the sights height over bore at 50 yards vs. 100? It seems like it should be somewhat relational...? As for the number of rounds fired, I used 5 shot groups for the 50 yard sight in, and when I saw what I was getting as far as groups at 100 yards, I shot an additional 5 shots to get a larger picture of where it was putting the rounds... I have to take into consideration that this is an Aimpoint with out magnification, and its a 4 MOA red dot, so I am not going to get truly representative groups at the 100 yard mark, but was just trying to get an idea of where I would be at on paper at that range. Thanks for everyones input so far... |
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The height of the dot over the bore will be approx. 2.68" which is why if you use a 50/200 yard zero you'll see a + or - trajectory of roughly 2.68" (often stated as 2.5").
Keep in mind that a 4 MOA means your red dot will cover roughly 4" at 100yards. So if your shots are within 4" group you are doing pretty good. S/F |
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I developed a mid range load for practice . . . You need a chronograph. If your "mid-range" load is shooting significantly slower than "standard load" ammo, you'll need to dial in more elevation to zero at fifty yards. Because of this increased elevation at fifty yards, you're putting more of an "arc" on the bullets trajectory, which results in the higher point of impact at 100 yards. Nonsense. http://www.box.net/shared/static/ksqu8yrsfd.jpg What do you use to create your charts? |
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The height of the dot over the bore will be approx. 2.68" which is why if you use a 50/200 yard zero you'll see a + or - trajectory of roughly 2.68" . . . False. The OP has repeatedly stated that he is using an Aimpoint in a LaRue mount atop an RAS II. This places the dot significantly higher above the bore than 2.68”. Even if the dot were only 2.68” above the bore, the height of the sight above the bore does not magically equate with the maximum ordinate of the trajectory. Even if he was using XM193, one of the highest velocity 55 grain loads commonly available, a sight height above the bore of 2.68” would give him a maximum ordinate of only 2.2”. 
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Keep in mind that a 4 MOA means your red dot will cover roughly 4" at 100yards. So if your shots are within 4" group you are doing pretty good. The accuracy level obtainable with a red dot sight is not limited to the size of the dot. The 10-shot group pictured below was fired at a distance of 50 yards using an Aimpoint ML2 with a 4 MOA dot. The group has an extreme spread of 0.548”, which is only slightly larger than 1 MOA. 
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I developed a mid range load for practice . . . You need a chronograph. If your "mid-range" load is shooting significantly slower than "standard load" ammo, you'll need to dial in more elevation to zero at fifty yards. Because of this increased elevation at fifty yards, you're putting more of an "arc" on the bullets trajectory, which results in the higher point of impact at 100 yards. Nonsense. http://www.box.net/shared/static/ksqu8yrsfd.jpg What do you use to create your charts? Oehler's Ballistic Explorer. |
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Quoted:Is there something I am missing or does this seem abnormal? I was expecting this to be much closer to 1" high at 100 than 2.5-3"... just trying to get an idea of where to start to correct this.
Keep in mind that the higher your sights are above the bore, the higher your 100yd impact point will be from a 50yd zero. Also, you didn't mention how many rounds you used for your groups. If you shot 3-round groups at each distance then you could easily see an extra inch or so difference between the two centers just because of random variance. Ten round groups are better for verifying zeros. Buck_Naked, pay attention to this man, for he knows of what he speaks. So if I am running an Aimpoint that co-witnesses the sights in the lower third, that height over bore would be added to the approximate 1.5" trajectory that the chart shows? Whats the difference between the sights height over bore at 50 yards vs. 100? It seems like it should be somewhat relational...? As for the number of rounds fired, I used 5 shot groups for the 50 yard sight in, and when I saw what I was getting as far as groups at 100 yards, I shot an additional 5 shots to get a larger picture of where it was putting the rounds... I have to take into consideration that this is an Aimpoint with out magnification, and its a 4 MOA red dot, so I am not going to get truly representative groups at the 100 yard mark, but was just trying to get an idea of where I would be at on paper at that range. Thanks for everyones input so far... If you want accurate calculations, the first thing you need to do is break out the calipers and determine the exact height of your sight above the bore. Then you need to fire multiple 10-shot groups at 50 yards to confirm your zero and determine your level of variation. Also, it would be a plus if you could find someone with a chronogrpah who would let you run 10 shots of your load over it. |
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OK. Lower velocity doesn't cause a projectile to drop faster than a faster projectile. I'll just shut my brain off now. Both slow and fast projectiles actually drop at the same rate; it's just that slow projectiles take longer to get to a given range so they have more time to fall. But even though you have to use more elevation for a slower bullet for a 50 yd zero, it will still have a lower impact at 100 yds than the faster bullet because it's got more time to drop. There's a different phenomenon that causes slower bullets to hit higher than faster bullets at short range, for a given zero, but that's due to internal ballistics issues, and doesn't really apply to the trajectories of slow bullets versus fast bullets that are zeroed at the same distance. |
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OriginallyThe accuracy level obtainable with a red dot sight is not limited to the size of the dot. The 10-shot group pictured below was fired at a distance of 50 yards using an Aimpoint ML2 with a 4 MOA dot. The group has an extreme spread of 0.548”, which is only slightly larger than 1 MOA.
Holy crap! What gun was that 10 shot group shot from and was it clamped into a bench? |
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I don't currently have a chronograph. Then it's not really safe for you to be developing loads. Get a chrony. If the load is well below listed maximums, why would this be unsafe? I understand the value of a chronograph, and its on my list, but the election has shuffled my list around as to what I purchase and when... at least for now... |
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I don't currently have a chronograph. Then it's not really safe for you to be developing loads. Get a chrony. If the load is well below listed maximums, why would this be unsafe? I understand the value of a chronograph, and its on my list, but the election has shuffled my list around as to what I purchase and when... at least for now... We all seem to be suffering from involuntary priority shuffling in the last couple months 
A guy at the range I used to shoot at damaged his hand when handloads blew out the bottom of his Lee Enfield. Another time a guy next to me was complaining about difficult extraction on his handloads. He didn't have a chrony either. The manuals all recommend you start at the minimum and work your way up, checking as you go. I am not a reloading expert by any means, so I follow the safety guidelines pretty carefully. |
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