Unlicensed Dremel
Moderator
OK, so I use ballistic calculators, but I'm not sure how to answer this question.
My friend wants to know this... looking out his back door, there's a tree - let's say that it's right at 200 yards (it's close to that).
He bought a laser boresighter.
Rifle is 16" bbl, 5.56x45 with M193. Assume 3075 fps and .233 BC, 70 deg F, 800 ft elevation. Assume line of sight starts 2.5" above bore line.
He wants to know, withOUT actually shooting, if he put the laser on that tree in the dark or on a cloudy day, and starts adjusting the reticle, where his crosshair should BE, to make a hit at that range. Should they match precisely or what, he asked.
Now, the answer is no, they shouldn't match precisely; that he will want the crosshairs BELOW the laser dot, to try to zero at that range (ignoring windage for the moment), since the laser represents the bore/ bullet path which doesn't act like a laser much past 75 or 100 yards, but by how much?
Evidently he just wants this as a temp measure until he can get to the range for full sighting....
Lasers boresighters aren't really made FOR that - they're fine for what they're intended -matching up exactly at 25 or 50 to get you on paper. But I don't know how to "make" my ballistic calculators calculate this number.
I suspect, just kind of eyeballing things, that the answer is that he will want his crosshairs to "show" on the distant target about 3.0" to 5.5" below the observed laser dot (would be more if the line of sight was less than 2.5", I think) - just not sure if this is even calculable, or how one would do it.
Edited to add: After some more thought, I came up with this: The Max height of the bullet path is +1.63 at about 125 yards, with a 200 yard zero. With a 2.5" differential at the muzzle, this means the bullet has risen a total of 4.13" in 125 yards (62.5% of the way to the target), before it starts dropping. Now *assuming* the bullet has acted EXACTLY like a laser to this point of 125 yards (which is hasn't but it's fairly close so let's pretend), or 62.5% of it's way to the target, if it would *continue* to act like a laser from there on out the last 37.5% of it's way to the target (75 yards), then it (the actual laser or laser-bullet) would rise another 2.608". Now, it's only 1.63" above the line of sight at 125 yards, not 4.13", so add 1.63 to 2.608, you get a 4.238" height over line of sight at 200. I'd say, round it UP to 4.5" in order to account for the gravity "drag" on the bullet from 0 to 125 yards.
Sound about right? Thanks. More of a hypothetical exercise than anything.
Of course I told him to "get thee to the range", but ya know....
My friend wants to know this... looking out his back door, there's a tree - let's say that it's right at 200 yards (it's close to that).
He bought a laser boresighter.
Rifle is 16" bbl, 5.56x45 with M193. Assume 3075 fps and .233 BC, 70 deg F, 800 ft elevation. Assume line of sight starts 2.5" above bore line.
He wants to know, withOUT actually shooting, if he put the laser on that tree in the dark or on a cloudy day, and starts adjusting the reticle, where his crosshair should BE, to make a hit at that range. Should they match precisely or what, he asked.
Now, the answer is no, they shouldn't match precisely; that he will want the crosshairs BELOW the laser dot, to try to zero at that range (ignoring windage for the moment), since the laser represents the bore/ bullet path which doesn't act like a laser much past 75 or 100 yards, but by how much?
Evidently he just wants this as a temp measure until he can get to the range for full sighting....
Lasers boresighters aren't really made FOR that - they're fine for what they're intended -matching up exactly at 25 or 50 to get you on paper. But I don't know how to "make" my ballistic calculators calculate this number.
I suspect, just kind of eyeballing things, that the answer is that he will want his crosshairs to "show" on the distant target about 3.0" to 5.5" below the observed laser dot (would be more if the line of sight was less than 2.5", I think) - just not sure if this is even calculable, or how one would do it.
Edited to add: After some more thought, I came up with this: The Max height of the bullet path is +1.63 at about 125 yards, with a 200 yard zero. With a 2.5" differential at the muzzle, this means the bullet has risen a total of 4.13" in 125 yards (62.5% of the way to the target), before it starts dropping. Now *assuming* the bullet has acted EXACTLY like a laser to this point of 125 yards (which is hasn't but it's fairly close so let's pretend), or 62.5% of it's way to the target, if it would *continue* to act like a laser from there on out the last 37.5% of it's way to the target (75 yards), then it (the actual laser or laser-bullet) would rise another 2.608". Now, it's only 1.63" above the line of sight at 125 yards, not 4.13", so add 1.63 to 2.608, you get a 4.238" height over line of sight at 200. I'd say, round it UP to 4.5" in order to account for the gravity "drag" on the bullet from 0 to 125 yards.
Sound about right? Thanks. More of a hypothetical exercise than anything.
Of course I told him to "get thee to the range", but ya know....
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