Darn, I don't know where some of you learned ballistics - but it sure wasn't in Physics class.
If you zero'd at 25 yd, you're going to be shooting low at 50-150 yd IIRC.
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No you would be shooting HIGH (roughly 2" high). The bullet was low PRIOR to 25y, after that it's on a steep trajectory.
What was that shortcut? 50yards=200?Meters
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With an M4 using M855 - though it's pretty close with M193, 68gr, 75gr with barrel lengths between 14.5" & 16" (not too far off for the 20"ers either).
If you are dead on at 25 yds. you will be very close at 100
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No, not even close. At 25Y with an AR-15 you will 6"+ at 100y (and the bullet will still be rising).
but if your zero is at 25 you should be zero'd at 300 yards which would put your bullet impact high at everything in between. Someone please correct me if I'm wrong.
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That was the theory, but you have to remember several things.
1) It was METERS not yards
2) You had to adjust the rear sight (to 8/3 +1 for the M16A2/ 6/3+2 for the M16A4)
3) Even then it didn't work.
That is why the USMC went to zeroing their rifles at 36
y because it gave a true 300
M zero.
If you aim center of mass with a 25 yard zero you'll hit a man out to 300 yards, thats the logic behind that training. However, you will hit 16.5" low at 300 yards.
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Note the military NEVER zeroed at 25 yards - it's always been 25M for the M16 series (unlile the USMC 36y came out). However, even with a 25y zero
yes with a COM aiming point you can hit a full sized (E type) target out to 300y. Note at 250y the round will be 12" high (in the head) so you better not have lots of drift.
At 300y your round will be 11.2" high, at 300M the round is still 10" high, and the round doesn't cross the line of sight till 435yards or so. (assumes a 25y zero with M855 from a 20" barrel - M193 drops a bit quicker but still doesn't cross til 415y or so)
For the most part shooting dead on at 25 yards is going to take the bullet high until around 125-150 yards or so then it'll drop below. I don't have my calculator handy.
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Negative, shooting dead on at 25y with .223 keeps the bullet high to the 400y mark (give or a take a couple dozen yards based on the bullet & barrel).
Back when we had M16A1s we used to zero by shooting at 25M (27.3 yards) with our
Long Range Aperture - which gave us a nice 375M long range zero. By flipping back to the unmarked aperture we got a 43M/250M battlesight zero (which is remarkably close to the 50y/200M zero...). The devil is ALWAYS in the details (like fliping apertures or setting the elevation to a higher setting....).
For 99.8% of AR-15 shooters using standard iron sights or optics mounted on the flattop your best zeroing option is to zero at 50 yards. That gives you minute of beer-can from muzzle to 225yards or so with most ammo types. (just re-zero when you change loads). Don't have a 50 yard range? Then there are two other options:
1) At 25yards zero so the bullet strikes roughly 1 1/4" below the point of aim.
2) At 100Y follow Beekeepers note that the bullet should strike roughly 1 3/4" to 2" over the point of aim.
As always it's best to fine tune at 200M (note at 200Y the round should strike roughly 1" high in a perfect environment - dead on is 'good enough' )