Or is it BS0 for 7.62? Z. Definitely Z.
OOoooo that’s a good blog post from CTD and got me a thinking about that Battlesight Zero and how it applies to me (ie someone loathe to get a 5.56 rifle…)
Sum up:
There is a rule of thumb for zeroing the M16 5.56. If you are zeroed at 36 yards, then you are zeroed for 300 yards. The reason is the sight line is above the barrel by a certain amount, and the sight line is straight while the bullet path is arched, so there are 2 places the bullet path intersects the sight line. At 36 yards and 300. (Only at 36 yards/30 meters and 300 yards/meters) So the space the bullet flied BETWEEN 36 and 300 in this system is all above the sight line. You are shooting a little high. How high? Almost 8 inches! Fine in battle when aiming at a bad guys center mass. Not so good if all you have to aim at is the head from the eyes up peeking out at you for a foxhole 126 years away. You could shoot clean over the enemy’s head.
So what is the Battle Sight Zero for the M1A/M14? Aha! I need to check.
I had a rules of thumb here, but I am now questioning that a bit.
Ideally, I need to find this chart, but for my rifle.
According to an M14 old manual, (found here, a source of MANY manuals) 25 meters was the BZ0 for a 250 meter (page 95 of M14 & M14A1 Rifle and Marksmanship) target. This presumes identical military ammo and same length barrel, sight plane height, etc. etc.
Sheesh, it’s taking me years to dope this out when the info is given away for free in just a few weeks time. All I’d have to do is go to Basic Training…
Anyhoo. Presumably, you want to go to the range with your M1A, shoot at zero for 25 yards. When you shoot at the 100 yard target you should be a bit high. If you HAVE a further away target… your rounds should be approaching center at 200 yards, but still high, and be spot on again at 250. This would all be better if you can use meters instead of yards…
And you might want to set your close in zero distance to something like… 36 meters so your far out zero is something like 300. Hmph. I need to study any ballistic tables I can find. Wait right here…
yeah, my rule of thumb seems less wrong. According to this, the ‘come up’ of clicks, assuming a 100 yard zero, is 17 click above that zero. Come up of 300 is only 5.
Again, just guessing, it seems to me, based on that ballistic table, it would be 15 and 3 up clicks if you zeroed at 200 and wanted to shoot to 600 and 300 yards, respectively. But a shot at a guy at 100 yards or so might be 4” highish.
But look at the difference in the METERS chart. Up 21.6 clicks for 600 meters, while only 17 for 600 yards… If I look at these too long I will get confused…
And you can see the differences in bullet weight in the charts here.
If I am reading that right, if you have a 180g 7.62 spitzer, your zero at 259 means the shot will be 2.8 inches high, and the highest it will ever get is 3 inches at 125 yards. The lighter bullet has a faster speed and flatter trajectory. But not THAT big a difference. Not with iron sights. Not for outside a real sniper school. Crawl before you can walk, T-Bolt. Well, at this point, it’s walk before you fly.
OOoooo that’s a good blog post from CTD and got me a thinking about that Battlesight Zero and how it applies to me (ie someone loathe to get a 5.56 rifle…)
Sum up:
There is a rule of thumb for zeroing the M16 5.56. If you are zeroed at 36 yards, then you are zeroed for 300 yards. The reason is the sight line is above the barrel by a certain amount, and the sight line is straight while the bullet path is arched, so there are 2 places the bullet path intersects the sight line. At 36 yards and 300. (Only at 36 yards/30 meters and 300 yards/meters) So the space the bullet flied BETWEEN 36 and 300 in this system is all above the sight line. You are shooting a little high. How high? Almost 8 inches! Fine in battle when aiming at a bad guys center mass. Not so good if all you have to aim at is the head from the eyes up peeking out at you for a foxhole 126 years away. You could shoot clean over the enemy’s head.
So what is the Battle Sight Zero for the M1A/M14? Aha! I need to check.
I had a rules of thumb here, but I am now questioning that a bit.
Ideally, I need to find this chart, but for my rifle.
According to an M14 old manual, (found here, a source of MANY manuals) 25 meters was the BZ0 for a 250 meter (page 95 of M14 & M14A1 Rifle and Marksmanship) target. This presumes identical military ammo and same length barrel, sight plane height, etc. etc.
Sheesh, it’s taking me years to dope this out when the info is given away for free in just a few weeks time. All I’d have to do is go to Basic Training…
Anyhoo. Presumably, you want to go to the range with your M1A, shoot at zero for 25 yards. When you shoot at the 100 yard target you should be a bit high. If you HAVE a further away target… your rounds should be approaching center at 200 yards, but still high, and be spot on again at 250. This would all be better if you can use meters instead of yards…
And you might want to set your close in zero distance to something like… 36 meters so your far out zero is something like 300. Hmph. I need to study any ballistic tables I can find. Wait right here…
yeah, my rule of thumb seems less wrong. According to this, the ‘come up’ of clicks, assuming a 100 yard zero, is 17 click above that zero. Come up of 300 is only 5.
Again, just guessing, it seems to me, based on that ballistic table, it would be 15 and 3 up clicks if you zeroed at 200 and wanted to shoot to 600 and 300 yards, respectively. But a shot at a guy at 100 yards or so might be 4” highish.
But look at the difference in the METERS chart. Up 21.6 clicks for 600 meters, while only 17 for 600 yards… If I look at these too long I will get confused…
And you can see the differences in bullet weight in the charts here.
If I am reading that right, if you have a 180g 7.62 spitzer, your zero at 259 means the shot will be 2.8 inches high, and the highest it will ever get is 3 inches at 125 yards. The lighter bullet has a faster speed and flatter trajectory. But not THAT big a difference. Not with iron sights. Not for outside a real sniper school. Crawl before you can walk, T-Bolt. Well, at this point, it’s walk before you fly.
And now why did I care about a 180 grain projectile? Most surplus stuff is the 150 or so. The MATCH stuff is the 180. But I can relax a bit. I'm not attempting to get hits at 300 yards with iron sights where I will care much about the 1 inch difference in a battle zero.
Now I’ve come full circle. MBtGE doesn’t sweat the details of ballistics. He was shooting his .308 for deer meat. HIS rule of thumb is a couple inches high at 100 and he can hit within a few inches of bullseye from 0-300 yards. And now I see it on paper. So... battle zero and hunting zero end up being about the same thing...
Anyway, going forward... there is a modified battle zero, the improved battlesight zero or IBZ0. You zero at 50, and are also right on at 225, with less variance of rise and drop at the other ranges until you get up past 300. All this low range zeroing is useful when your local shooting establishment won't let you do anything but shoot to 100 or so yards and from a bench.
Now I’ve come full circle. MBtGE doesn’t sweat the details of ballistics. He was shooting his .308 for deer meat. HIS rule of thumb is a couple inches high at 100 and he can hit within a few inches of bullseye from 0-300 yards. And now I see it on paper. So... battle zero and hunting zero end up being about the same thing...
Anyway, going forward... there is a modified battle zero, the improved battlesight zero or IBZ0. You zero at 50, and are also right on at 225, with less variance of rise and drop at the other ranges until you get up past 300. All this low range zeroing is useful when your local shooting establishment won't let you do anything but shoot to 100 or so yards and from a bench.
3 comments:
Battle Zero is a quick and dirty, but it DOES work!
I use JBM Ballistics for my calculations for a MPBR or BZO for any rifle. All you need to know is the bullet length and ballistic coefficient (.416 BC and 1.125" bullet length for 7.62 NATO) bullet weight (146.6) muzzle velocity (normally around 2,750 but may vary with your barrel length) barrel twist (normally 1:12 or so) and sight height (for me: 2", yours may vary, but it's important to get this number right as the sight height plays a very critical role in the computation of a BZO for your rifle).
You can play around with the numbers such as your vital zone radius (I prefer about 7") and the Zero range (300 yards or so) to get the best MPBR (Maximum point blank range).
For the numbers given above for a 7.62 round fired out of a scoped rifle with an 18" barrel, we get a zero at 25 and 300 yards with a maximum rise of 5.8" at 180 yards and a MPBR of 381 yards (7" of drop).
T-Bolt: Have you tried WRSA? Here is a link I found there which might help.
http://www.archive.org/details/How_to_Shoot_the_US_Army_Rifle/How_to_Shoot_the_US_Army_Rifle.pdf
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