If that's the case, just zero to 250 yards. That will get you there with almost all ammunition and barrel lengthsQuote:
Originally Posted by 4thPointOfContact
If that's the case, just zero to 250 yards. That will get you there with almost all ammunition and barrel lengthsQuote:
Originally Posted by 4thPointOfContact
It's really close to a 25 meter zero.Quote:
Originally Posted by 4thPointOfContact
That would be a 100 yard/meter zero, with POI 2.5 inches high.Quote:
Would it be confirmation if I were to zero at 2.5 inches high at 100 yards/meters?
I think you are misunderstanding.Quote:
But you've brought up another conundrum, why is there 'no confirmation at actual distance' when zeroing at 37 meters and putting a group on a target at 50, 100, 200, or 300 meters and there is 'confirmation at actual distance when zeroing at 50, or 100 (or pick your favorite) and putting a group on paper at 50, 100, 200, or 300 meters? Or, am I just misunderstanding what you said?
Your Point of Aim/Point of Impact (POA/POI) data is only guaranteed at the distance you actually shoot, but whatever actual distance you shoot can be your zero. If you want a 250 cubit zero, zero at 250 cubits, or a verified offset at 100.
When you have optics that are not zeroed (no verified POA/POI data), it is common to conduct initial zero at 25 meters (feel free to substitute "yards" in your mind if you choose).
Initial zero at 25 will get you on paper at longer ranges, allowing you to refine the zero.
Jumping straight to 100, 200, 300, 432, whatever, will generally be a waste of ammo, and potentially unsafe. Waste of time and ammo as it will be difficult to figure out where impacts are unless you have a spotter with a high magnification optic, and unsafe since those misses may be excessively high, resulting in projectiles going over the containment feature, or excessively low, causing them to ricochet over or around the containment feature.
If you go for POA/POI intersection at 25, you will be fairly close at 300.
At 25 1.5 inches low will get you close at 100, and 1 inch low will get you close at 200.
One dude went through a lot of trouble to make a bunch of offset 25 targets to aid this effort:
https://www.m4carbine.net/showthread...t-EOTech-etc-)
Personally, I don't use them, as I know what 1.5" looks like. For those that don't do this all the time, dedicated targets can make the process easier.
Once you are pretty much on the correct offset at close range, finalize your zero at actual distance.
The reason for this is that different guns, different ammunition, different environmental conditions, different line of sight (LOS) over bore height, and other variables are individual and cannot be 100% captured on the exact close-range offset needed to guarantee longer distance POI.
Even if you can precisely match the trajectory and extrapolate the 25 POI for your exact environmental conditions, slight variations in perception, spin drift, sight offset, etc, pretty much guarantee that further sight adjustments will be needed to get a high-confidence POA/POI at actual distance.
Another issue is that as zeroing distances get closer and closer to the muzzle, errors in trajectory at longer range are magnified.
If you want a 200 zero, with 100% accurate ballistic data, and you think that you are starting at 25 but you are actually at 20, your zero will be about 1/3 of an inch higher than intended. Not a big deal if you then go out to range and confirm/refine, much bigger of a deal if you don't, as your path will be closer to a 260 meter zero. This can make for all kinds of confusion in different applications if the user is working off of holds based on a 200 zero.
A limiting feature is that most folks do not have easy access to a 200 or 300 meter range, which is why many will choose a 25 or 50 zero.
This is, however, why I really like a 100 zero. The trajectory intersects the point of aim for a long time with 5.56 at over 2700 f/s; from 90 to 115 meters, the trajectory is within 0.2 inches of the line of sight, depending on actual velocity. This gives a very open window for ranging error during zeroing, and reduces the effect of immobile targets/firing positions commonly found on public ranges.
A zero is a personal choice.Quote:
I don't really care if the zero range is measured in feet, yards, chains, cubits, meters or even Smoots.
What I do care about is having the best ability to put a shot center mass at the widest range of .... ranges, neither too high nor too low with just a glowy red dot as my aiming point. If the trajectory never rises more than 3" nor falls more than 3"below POA all the way out to 250 yards I'll be a happy camper. The chances of being engaged by someone past that distance are practically nil, and much less for me as a civilian now.
I base my choice of zero on application.
In my experience, the ability to hit small targets from 5 to 75 meters is critical, and the least amount of thought I have to put into getting that hit, the better. Being able to accurately place rounds at 75 to 150 is the next most important task, and the ability to effectively hit torso targets at 150 to 300 closely follows that.
Different ammo choices, different guns, different optics, and different applications will change which zero is selected. That could be a thread on its own, and I've already blathered on enough.
I'd recommend checking out the various zero threads:
https://www.m4carbine.net/showthread...d-Trajectories
https://www.m4carbine.net/showthread...100-Meter-Zero
https://www.m4carbine.net/showthread...ttlesight-Zero
Notes:
-The human behind the gun is the single most significant factor.
-A simple ballistic arc does not capture dispersion at range, build in room for error.
-There is no rule that says that you must have POA/POI intersection at your zero distance. All you must know is where the bullets go in relation to your point of aim at a specific distance. That's a zero. POA/POI intersection gets a lot of people all wound-up over nothing. I like to use 100 yards/meters as a zeroing distance (not always POA/POI) as it irons out a lot of error.
-Data from target engagement is more important than how you zero, as that data builds other zeroes (known POI in relation to POA at a specific distance). Just make sure that what you think is your baseline is truly your baseline.
Oh, JBM is a good free ballistic calculator with a lot of good BC data for common projectiles.
http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi
For more advanced stuff, Applied Ballistics is phenomenal.
Excellent thread .
Of specific interest to me was how this representation
really shows how the impacts at various ranges get closer
with heavier bullets in a 16 inch barrel .
Specifically with the 50 yard zero .
I'm still in the 50 yard zero camp for Aimpoints .
I've considered the 100 yard zero many times but
keep coming back to the 50 .
Does any one have the math as to how much the
impacts are changed with an optic versus irons ?
Specifically for Aimpoints with a lower 1/3 co-witness
as they would be slightly further from the barrel .
It's pretty much not a factor.Quote:
Originally Posted by Cobrasks
Here's an example:
2700 f/s M855
200 meter zero
2.5" LOS over bore (iron sight height):
50 meter impact: .63" high
100 meter impact: 1.96" high
3" LOS over bore (optic too high to cowitness):
50 meter impact: .25" high
100 meter impact: 1.71" high
As you can see, the closer zero magnifies the effect of the sight height difference, and even then, the difference is negligible.
For reference, with AR pattern rifles, top of rail is right around 1.2 inches above bore.
A rail-mounted front sight will be between 1.2 and 1.5 inches above the rail (depends on how far in/out it needs to be to achieve zero).
Ballistic calculators use the distance between the line of sight and the muzzle (this will be important in a second).
The sight offset is therefore 2.4-2.7 inches over bore. I usually use 2.5 inches for iron sights.
A standard height 1.5 inch optic base generally gives a 2.6-2.8 inch height, depending on tube thickness, once zeroed.
Lower 1/3 cowitness sights are usually 1.6 inches above rail (to center of glass), for 2.8, but it's a little less at the muzzle.
A NVG height non-cowitnessing sight will be about 1.9 over rail, for a 3.1 inch offset, closer to 3 at muzzle.
For simplicity, I use the following:
Irons and absolute cowitness optics: 2.5"
Lower 1/3, and optics in standard 1.5" mounts: 2.7"
NVG Height/High Mounts: 3.0"
And really, if you're using a 100 yard/meter or further zeroing concept you can just use 2.7 across the board and be just fine out to 1,000 meters without having data confliction.
So how much variation would there be between a 10.5" and 12.5 " barrel with these zeros? The 25yd looks interesting for my 12.5" build.
This is all great info. I will tell you this. When we zeroed the M16 at 25 meters and aimed center mass, the 55 grain round was low at 300 meters. You wanted to hold high at 300.
I have always observed that the "short range zero" is just a starting point. It will be Minute Of Bad Guy, but that's about the only assurance.
I HAVE to verify at distance with the individual rifle/carbine to KNOW if it's ON.
What happened to the graphics on this thread?? I remember there being POA and POI shown on IPSC targets. They were a very helpful resource. Hopefully they're not gone forever?
They're still there, page one.
You know, I was out shooting yesterday, two rifles zeroed for my 62gr load, but shooting 75gr BTHP, with an obvious, expected, and acceptably differing POI at 50, 100, and 225 yards.
It occurred to me, it'd be great to see graphics of, for example, an 18" rifle, which is zeroed with m855, with graphic that demonstrates where the POI for, say, mk262 would then be at different ranges, etc.
I can visualize it, but no way am I smart enough to make one.
Hmm...this is what it looks like on my computer...Quote:
Originally Posted by ViniVidivici
https://i.imgur.com/DL6zTFI.jpg