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The 36-yard Zero

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59 minutes ago, ARTrooper said:

 what's the math to figure all this out with what you are using?

JBM Ballistics "Trajectory" calculator (not the "simplified" version).  You'll need to play with your numbers and find the best "Maximum Point Blank Range."

That calculator will allow you to input your vitals diameter (5", 7", whatever).  Check the block that says "Zero at Maximum PBR" so that data gets included in the output chart. 

MPBR will be a distance, say something like 364 yards.  Say you chose a vitals diameter of 5".  That means that you can dead-hold your sights out to 364 yards, and the projectile isn't gonna leave that 5" area during it's flight...

Edited by 98Z5V
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2 hours ago, 98Z5V said:

EDIT - here it is as a.pdf, brother...

Much appreciated Brother! The printer is spitting out a stack of 50 as I type!

I really like this for a zero. 55 grain is my normal go to round so it will be perfect for several of my rifles. I need to do the math on the app and see what the best zero will be for some of my other rifle/ammo combos.

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  • 3 weeks later...

For the iron sights on the 16" Grendel M4, I came up with this data, and made my iron-sight zero to this last weekend.

Ran out all the math for the 16" best iron-sight zero distance, and came up with this, for 25 yards. This looks the best, of everything I made as inputs.  I'm talking individual yards for different charts.  Max of less than 7" at a 25-yard zero, out to 300 yards.  Even one yard either way (off 25) opened that up.



Knocked out the zero this morning on the gun.  Functionally, it ran like a champ, with zero functional issues whatsoever.  The first few rounds got kinda scratched up brass, but that smoothed out in the next 10 or so rounds.  Sharp edges on the barrel extension?  Probably was, until it got beat on a little. 

Since the dope chart above works out to 0.2" low at 300 yards, with a 25-yard zero, I set the MaTech rear sight at 300 yards to dothis 25-yard zero.  It adjusts from 200 to 600 in 100-steps, and it's got a 350 step in there, too.  I know if I don't touch anything, I'm 5.2" high from point of aim at 100 yards, 6.6" high at 150 yards, and 6.3" high at 200 yards.  I have the option to drop that sight back to the 200-yard setting, and it'll get better.  I didn't do that today, and check what kind of an effect it had, because I only set out targets at 25 yards (for zero) and 100 yards to see how it does on steel.

At the 25 yard target, it was only paper zero target.  I came up with this for a zero, on a clean target, and I gave it one more click right after this group, then cluttered the target all up with another mag.  I'll take it.  :thumbup: At 25 yards, I would have liked to see them all touching, but I was literally a combination of hungover, jacked on coffee this morning, shooting iron sights on a table with a front bag and no rear support. 



In that trajectory chart above, I'm a max of 1.4 mils high at 100 yards, 1.7 mils low at 450 yards, and dead-on at 300 yards, as far as holdovers.  Out to 300 yards, it's at 6.6" high at 150 yards at is highest flight path, and 0.2" low at 300 yards, giving me a 6.8" trajectory spread out to 300 yards with irons.  I'll take that.  :thumbup:

Edited by 98Z5V
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