Why I use a 100 yard zero.

[Rastoff]

I posted this in another thread, but I think it deserves its own thread. This is intended for as broad an audience as I can hit so, I'm including some basics on trajectory.

Hitting your target is all about understanding the trajectory of the bullet. Trajectory is the path the bullet follows toward the target.

Since gravity works, the bullet doesn't travel in a straight line.
Because the sights are higher than the bore, the barrel will need to be angled up a little in order to hit the same point you're looking at.
Because the barrel is elevated in relation to the line of sight, and because the bullet travels in an arc, there are two points of convergence where the line of sight and the path of the bullet are the same. Look at this picture:

Line of sight is referred to as Point-Of-Aim (POA).
Where the bullet impacts the target is Point-Of-Impact (POI).
So, a simpler way to state it is POA=POI at two points along the trajectory. This is true with every distance you zero at unless you zero at the apex of the trajectory.

Now let's do some real math. Here is an example of zeroing at 50 yards. With a normal AR and a sight height over bore of approximately 2.5", this is what the trajectory will look like:

Notice that at 50 yards and ~235 yards the bullet path crosses 0. This means POA=POI at those two points. The problem with this is everything between 50 and 235 will hit higher than POA. That means you'd have to hold under for those ranges. Everything closer than 50 and further than 235 will hit lower than POA. This means you'd have to hold over for those ranges. I know it's only 2" either way, but that translates to a 4" spread and some are high and some are low.

Change that to a zero at 100 yards and we get this:

Notice that there is only one place where POA=POI in this chart; 100 yards. Also notice that from 0 to ~205 the POI will be anywhere from 2.5" low to 0. This means that at any distance other than 100 yards, you'd have to hold over a little. At no time will you ever have to hold under. This simplifies the aiming from 0-200 yards because you know your round will hit within 0-2.5" low. That's only a 2.5" total spread.


So, the question comes down to, how often will you shoot beyond 200 yards? If you shoot past 200 a lot, then the 50 yard zero might be for you. If you're like me and never use an AR to shoot beyond 200 yards, and only rarely shoot beyond 100, the 100 yard zero makes more sense.

Anyway, that's why I zero at 100 yards.

 

[BC38]

Very well written and explained Rastoff. That very clearly covers a couple of aspects of the subject that I had never really considered. THANKS!

 

[eb07]

I am a fan of the 25yd zero for general use and shooting out to 400 but the 100 yard zero works great for hunting and is on my prairie dog rifle

 

[ChattanoogaPhil]

I use a 50yd zero. It extends the point and click usefulness of my red dot vs 100yd zero. For my use, agonizing over an inch or two above line of sight at shorter distances isn't a good trade for exaggerated variance at distance as the chart indicates to 300yds. It's not a matter of how much I practice beyond 200yds, but rather that the equipment is set to better accommodate if needed.

 

[YeshuaIsa53]

I agree with a 100 yard zero with my hunting rifles and .22 rifles. Most all my shots are fairly close in the swamps.

I also think a 25, 50, and 75 yard target to be invaluable for under 100 yard shots later, maybe with each rifle one intends to hunt with.

 

[Rastoff]

Phil,
I find that an interesting viewpoint considering the number of times you've mentioned that you'll rarely even shoot 100 yards.

 

[JVSIII]

Plusses and minuses to all, but we'll thought out reasoning. I currently use a 50 yard zero for red dots, my variables have BDCs, so they are sighted in per instructions at 100 to make them work properly. My opinion is to find a trajectory that works for you and learn it backwards and forwards.

There's the 37.5 (I think)yard zero that looks promising for those that like the 50.

Thanks for posting.

Sent from my Moto G (4) using Tapatalk

 

[ChattanoogaPhil]

Phil,
I find that an interesting viewpoint considering the number of times you've mentioned that you'll rarely even shoot 100 yards.

You must be thinking of someone else. The below is what I have repeatedly posted. But even if I only had 100yd range to practice at my reasoning for a 50yd zero would be the same.

For me... I practice shooting offhand at steel targets from 50 to 200yds.

 

[agksimon]

I have a Vortex Spitfire 3X, prism scope on my M&P Sport ll. The crosshairs have yardage lines out to 500, for 55 grain factory ammo. I have it dead-on at 100 yards and will eventually try it at longer distances, as soon as I can get to a 500 yard range. I wonder how close it will be. Anyone here ever tried one?

 

[scooter123]

I have three AR's, two with Iron Sights and one Precision Rifle with a scope.

For the Iron Sighted AR's I have the sights set for a 50 yard zero because with my aging eyes shooting irons past 50 yards can be a bit frustrating. Yeah, I know Irons can be effective at 100 yards even for my eyes, however I just cannot shoot tight groups with irons past 50 yards.

For my Precision Rifle I have the zero set for 100 yards because with the help of Optics and a good rest I can manage to group around 1/2 inch. I'll also occasionally shoot it at 200 yards, the maximum for the range I shoot at but when I reach out that far I just dial in 10 clicks on my elevation dial.

 

[vonn]

Good post,thanks. My feeling is that no matter what distance you pick to zero you need to practice at every distance you can to know where your rifle hits and to learn range estimation which for me is hard to get right.

 

[forrestinmathews]

As a guy who fired .223 first out of a bolt action, coming to the AR platform was a real eye opening experience. The jump from 1.5" above bore to 2.5" above bore has a real effect on the trajectory. For my bolt gun I use a 50 yd zero which gives me a 150 yard coincidental zero for 50 grain V Max. For the AR I did the battle sight zero of 25 meters and was less than impressed. I rezeroed at 42 meters and found much more happiness with a second zero at 220 meters. No idea why I did the AR in meters.

 

[ChattanoogaPhil]

Good post,thanks. My feeling is that no matter what distance you pick to zero you need to practice at every distance you can to know where your rifle hits and to learn range estimation which for me is hard to get right.

I use a 1x red dot on my AR. Range estimating and holdover isn't an issue-- just hold center and click. Any distance beyond what a 50yd zero would accommodate would also be beyond the expectations I have of my rifle. Point and click operation.

My rifles with magnified optics and mildot reticles I can estimate distance fairly well using objects/targets of known size. It's actually a fun practice. At the range where distances are of course known, I play around in reverse estimating the size of objects/targets. Good exercise for old brain.

 

[blues7]

I also opted for a 100 yard zero with my M&P15 TS.

The reasons, in addition to the sound discussion by Rastoff above are provided in this article by Kenan Flasowski on the Shooting Illustrated site.

 

[ChattanoogaPhil]

(above link)

"I am a big fan of the 200-yard zero, and it is very close to a 50-yard zero. My primary AR is zeroed at 200 yards, but I like to be able to engage out to the maximum effective range of the 5.56 NATO cartridge. With a 200-yard zero, the bullet does rise above LOS, but not more than about 2 inches at 120 yards, so holdunders are negligible, and the holdovers at 25 yards and closer are similar to the 100-yard zero. But I have the luxury of unlimited access to a 400-yard range. Many armed citizens may not get to train much and may not shoot at 400 yards—ever."

I agree with Kenan Flasowskl's comments in the first part of the paragraph above, both he and I use 50yd zeros on our primary ARs . I do not agree that you must have a 400yd range to set up your rifle with a 50yd zero (or 25yd or whatever), at least that's what he seems to be implying. ARs for self defense aren't set up to accommodate practice range facilities, but rather to accommodate the purpose of the rifle if and when the need arises away from the range.

As far as the rest of the article, I think Kenan spends WAY too much time fretting about 1-2in holdovers. In self defense situations, unless the bad guy is standing perfectly motionless like paper on a target stand, and the bad guy poses no immediate threat to you so you can diddle around with precise holdovers of an inch... forget about it.

 

[eb07]

If you are a hunter you should have a range card for your rifle/ammo anyway. So the zero really doesn't matter as long as you practice with it.

It's all preference.

There is the range card on my SCAR-17. Laminated and tucked into the stock, one quick tug and I have ranges out to 800 yards with scope clicks and holdover....

a good site to make these is here:

JBM - Calculations

 

[Rastoff]

You must be thinking of someone else.

Indeed, I must have been mistaken. Not the first time, won't be the last. Even so, I would think the -2" to 0 from muzzle to 200 yards would suit you well.

 

[Kadonny]

I use the 100 yard zero on my battle rifles for just as you said Rastoff, pure simplicity. All you have to ever remember is how much holdover is needed, if any, for ranges from 0 to 300 yards and even greater. Bonus is my ACOG is then zero'd at the recomended yardage (because of the reticle) so everything is the same for me on all my battle/SD rifles. Simplicity.

 

[Neumann]

There's nothing wrong with selecting 100 yards as the zero point, depending on the external ballistics. A high velocity round, like 5.56x45 or 7.62x51 probably better zeroed at 200 yards.

The offset between the scope and bore will shoot low at 100 yards, zeroed at 200. The closer you zero, the greater the deviation at longer range.

Slower rounds, like pistol caliber carbines, are best zeroed at 100 yards. They drop like a rainbow, and 100 yards usually gives you "deer accuracy" from 0 to 150 yards (- 7").

I use a program called "Ballistic" for iPad and iPhone for an objective estimate of external ballistics. Its tables show the deviation based on the ballistics, zero distance and offset. The software is $20 well spent.

 

[rockquarry]

An additional aspect bears addressing here. Some of us use different zeroing methods and techniques and we all have different skill levels. Comments are based on my experience only and I seek no argument.

I zero using a Hart pedestal rest with a Protektor sandbag and a Protektor bunny ear bag rear rest. I use handloads with a either a Sierra 69 MK or Sierra 65 GK and my observations are based on such loads rather than the 55 grain commercial loads that many shoot, though there are likely some similarities.

From the rest, I zero approximately 2" high at 100 yards for an approximate 200 yard zero. To closely simulate an actual "field" position, i.e., using less than a stable rest, I support the rifle forearm/ handguard with my left hand placed atop the forward sandbag.

This method, for me, consistently causes point of impact to be approximately 1 1/2"-2" low at 100 yards and 3"-4" low at 200. This could vary from shooter-to-shooter. The point is that it is worth checking as the variance could be significantly less or greater than what I have experienced.