TA DA!!!! for the first time in about a bazillion months, an AR15 related topic. YEA!!!
OK, most of us know that there is more than on zero method for our rifles and I am trying to decide on which to use.
The data I used for this was 55gr, 3033fps, 0.243BC, I don't remember the temp or elevation.
Site I used is: http://www.robsoft.nu/ballistik_en/ballistik.asp?MainID=3
And yes, I do understand that this is all really ballpark.
Apparently the military uses a 25m zero similar to the 25m zero used for M16, which gives them roughly a 300m zero.
The sights are designed around this method.
The 16 inch barrel on a range in yards with a slower velocity and only a 55gr bullet makes for a 25-369 yard zero.
It is not exact, but roughly enough.
At the highest point in its flightpath (about 210 yards), the bullet is a tad over 10 inches over the line of sight (LOS).
This method provides for a minimum of adjustment out to 600 yards where the bullet would be about 73 inches low.
Then there is the 50-200 yard zero suggested by LTC Chuck Santos; the Improved Battlesight Zero (IBZ).
This provides a flatter trajectory so the highest the bullet gets to is only about 1.85 inches high.
But at the 369 yards referenced above, it is more than 17 inches low.
At 600 yards it would be at -101 inches.
Apparently, if you adjust the sights per his instructions, you can still use the vertical adjustment on the A2 rear sight correctly.
I understand that a lot of SF guys are fans of a 100yd(or meter) zero.
That way the bullet never passes above their line of sight; it meets LOS at 100 yards then begins to fall again.
I don't think I like this one.
The reason is that it falls off FAST.
At 300 yards it's a foot low.
By the 600 yard line it is 111 inches below LOS.
If you have a whizbang sight with a bullet drop compensator that might be OK.
I am looking at using the irons on a detachable carry handle.
The other method I am considering is the Maximum Point Blank Zero.
For those that do not know, this method is the range at which the bullet rises to and crosses the LOS and rises above the LOS by the same amount which it started below then falls again to the same distance below the line of sight.
So, for a rifle with a sight line above bore of 2.6 inches, the bullet starts out 2.6 inches low, rises to 2.6 inches high and then falls again to 2.6 inches low.
The range at which it again hits 2.6" low is the Maximum Point Blank Range.
Using the above data, the bullet first crosses the LOS at 44 yards then climbs to a high of 2.67" at around 147 yards.
It then falls to cross the LOS again at about 239 yards and finally the MPBR at about 275 yards.
I think this might be my favorite method as it allows one to basically shoot where they want to hit all the way out to 275 yards; no adjusting for hold over or hold under.
At 200 yards the trajectory is 2.39 inches low; thisíll be important in a minute.
300 yards is only a little more than 5" low and out at 600 it is about 98" low.
Biggest problem with this is that you would zero and confirm at 44 and 239 yards, which in my experience, no ranges are laid out for.
Now for my question, does anyone know if I used the MPBZ method and set the rear sight at the 200 mark and confirmed at 200 yards that it is basically hitting at 2.4 inches low, would it be right (or close to it) at 300, 400, 500, & 600 yards?
I think it would/should.
I would check it when I could at the real distances.
What method do you irons guys use?
I've used the 25 yard out of habit and lack of spotting scope. I usually grouped at the bottom of the the little Army silhouette, this would allow me to aim center mass on all targets, pop up range, and the round would impact.
But the 50 is intriguing
I've run the 50m zero for about fifteen years or so with irons and CQB optics., it generally works, at least with anything in a range that you should be shooting a carbine with. If you are running an ACOG or something though, I will zero at 100M and use the appropriate hold overs.
I use the 25 m zero for my carry handle iron sights. My aim points & eotechs I use the 50 yd zero.
I prefer the 50 yard zero for duty/self defense ARs. I know at CQB it is pretty much on, (remembering the mechanical offset of sight over bore) within room distance and out to 100 yards it will hit approximately 1.1 inches high.
I used to set my guns up at 100 yard zero, and to tell you the truth, I really can't tell that much of a difference. Most 55 grain practice ammo is only good for about 4 MOA anyway. With match ammo I will notice the difference.
And not being a great distance guy, I don't train or teach much past the 100 yard mark anyway. That is what the state academy uses as well as the NRA for Police Carbine Instructor Certifications.
It is much, much easier to teach how to zero at 50 yards, let alone saves time and ammo for practice.
I guess my bottom line is this, magnified optics like ACOG, and variable powered optics I still like the 100 yard zero, and iron and red dot sights I like the 50.
Hope that helps.
I use the 100 yd zero on irons and optics as that was the way I learned and practiced. It is now second nature and I have yet to find a compelling reason to switch. I think an argument could be made for or against each of these methods and it is more important that a person picks one and sticks with it to master the technique. I could see it being problematic to change your zero technique frequently, which could increase confusion in stress situations.
I have a Trijicon TR-24g on a 16" carbine. I run a 50 yard zero and use the sight as Molon described here
. Works well for competitions at our IDPA club where the furthest we can shoot is 300 yards. Anything under 50 yards is will land somewhere in the triangle.
100 yard zero for anything non rimfire and sometimes it too... math on the fly is easier by multiplication or division of 100 as compared to any other number... powers based on ten are faster by a long shot...
100 yard except my AR pistol which is 25 wanting more point of aim point of impact up close.