36 Yard Zero

[Old Bob]

I ran across this video of a former special forces guy explaining different zeros for red dot/holographic sights. He shows how the 36 yard zero is the best option. Isn't this basically a point-blank zero?

https://www.youtube.com/watch?v=jttB1kUXfJE

[FRB6.5]

It is a form of one for a ~6" vital zone. It makes sense and works well for BUIS and red dot use.

[R2BRO]

25yrd seems to be best for 6.5G for ~7-9" coverage of 0-300yrd

[FRB6.5]

It is geared more towards 5.56 velocity. If you think about what is also ~6" in diameter it makes even more sense for that use.

[R2BRO]

yes that stuff geared towards 556 velocity, but..

if you zero 6.5G 123gr SST Hornady @ 25 yards (or @50 yards with 1.1" high), then you get 2.43" high at 100, -3.2" at 250yrd and -8.6" @ 300 yards.

[Klem]

I ran across this video of a former special forces guy explaining different zeros for red dot/holographic sights. He shows how the 36 yard zero is the best option. Isn't this basically a point-blank zero?

https://www.youtube.com/watch?v=jttB1kUXfJE

Yes, it's a PBZ, but won't be optimum for our calibre and loads.

JBM (online) has a PBZ facility in the program. Enter the diameter of the target and set the range increments to 1. You can use the distance where the bullet intercepts the sight line as your zero range, or note the offset at your normal zeroing range (say, 100yds) and zero to that.

[lazyengineer]

For a red-dot, I agree with this distance, and use similar. For a scope, I do not. I usually use 200 yard zero for typical scope zero, for 5.56 and similar; but not necessarily so for Grendel.

I once got burned using a ~200 yard zero with Grendel in a slow configuration system and load. With a 36 yard zero, just be aware of the similar. In my case, it meant my 100 yard zero was almost 3" high. And sure enough - I lined up a nice stabilize high neck-shot (per land-owner request) on a deer that we later clocked at 100 yards. The bullet skimmed right over it.

So just be aware not all of the 5.56 behavior necessarily translates to a Grendel that isn't a light 100 gr bullet out of a 20" BBL. It can have a bit more arc to it at the shorter ranges than one might be used to with 5.56 ballistics.

[R2BRO]

it is impossible to match xm193/55gr with 6.5G 123gr for trajectory. so Grendel will have another sweetspot, below are some snapshots for calculated 123gr Hornady SST from 18" barrel with 2" sight height:

zero @100


zero @50


zero @25


im undecided yet, will have to think about it. Also there will be variation for handloads of course...

[Sputnik]

How does different scope heigths figure into zeroing?

[Klem]

How does different scope heigths figure into zeroing?

Sputnik,

The higher the scope the steeper the barrel angle that needs to happen to intersect the bullet with the line of sight on the target. At further ranges it becomes less of an issue.

If you think of the scope as being a laser beam the dot on the target climbs as the scope height increases. To hit the higher dot you need more of an angle on the barrel.

[Sputnik]

Thanks Klem, so a 2.00 inch scope heigth verses a 2.75 inch scope height that intersects line of sight at 25 yards upward will each have a different intersection/zero down range as the trajectory falls back to line of sight again.

[Kswhitetails]

Correct Sputnik. FYI I believe the standard by which most AR M4 height mounts are considered is 2.7" if I recall correctly. Don't hold me to that, Google will tell you for sure, but inside 400, where 99% of AR kill shots occur, if I'm off my a quarter inch, it wouldn't matter. The azimuth change is so minuscule that it's within human abilities and almost indeterminable.

I personally use 2.7" in my calculators and haven't had to change anything to hit steel out at distance.

[Klem]

Sputnic,

Yes.

I use 2.5" for AR scope height and 1.6" for bolt gun scope height. CQB style red dots are sometimes preferred higher to avoid cramming your head down onto the stock.

A typical Grendel load is a 120NBT at 2460fps and the zero range, 100yds.
From an AR15 at 2.5" scope height the bullet will cross the line of sight twice; at 79yds and 100yds.
The same load from a bolt gun at 1.6" scope height will be 52yds and 100yds.

For those same load and guns above the elevation difference required to hit a target downrange is about 0.2Mil

[Sputnik]

KLem, thanks that makes sense. At the range, I try at 25 yards to hit approximately 1 inch low to get on paper at 100 yards (scope height 2.75"). I was amazed at your calculations that it takes 79 yards to cross line of sight and back again so soon at 100 yards.

[Klem]

Sputnik,

Here's a screen grab of what the bullet is doing every yard as it approaches the target at 100yds. The left hand column is Yards, the second is Mils and the third is inches. The bullet climbs to where it barely grazes the Line of Sight, crossing at 79 and then barely above it until 100.


I recommend JBM Ballistics online for this.