AR-15 Zeros And Trajectories
BY Herschel Smith
2 years, 6 months ago
Via WRSA, this thread at AR15.com is great. Thanks to the guy who worked so hard putting this all together.
I got it all the first time around (make sure to study all of the graphs and read the discussion carefully). If you’re unaccustomed to working with Newtonian physics, it may take you a time or two through it.
My complaint: He addresses only 55 grain bullets, and doesn’t seem to make much of barrel length. I’d like to see this thread expanded to include 68, 75 and 77 grains. A lot of guys are shooting heavier bullets now. That affects velocity, and thus changes everything.
But that’s a minor complaint. To be sure, I haven’t put together anything like this for readers, so I have no room to complain. I’m sure he put an awful lot of work into this, so he doesn’t need complaints from the peanut gallery.
On October 15, 2021 at 11:07 pm, RHT447 said:
Here’s a good companion video by Travis Haley–
https://www.youtube.com/watch?v=DFbpjNh4DBA
On October 16, 2021 at 1:36 am, Georgiaboy61 said:
The Improved Battlesight Zero was invented by a Marine Lt. Colonel Chuck Santose, so it is also sometimes known as the Santose method or system. As the lengthy post at AR15.com makes clear, its chief virtue is that it allows greater versatility out of the standard front sight and rear carry handle sighting system than is typically the case.
As the article notes, the standard battle-sight system employed by the AR15/M16 and its carbine derivatives, is designed around a 25-meter BSZ (battle-sight zero) for use inside 300 meters, with elevation adjustments made for longer ranges to be done using the elevation wheel, whether the fixed carry handle type 300-800 meters, or the detachable carry-handle 300-600 meter type. Inside 300m, the standard BSZ was to be used, combined with the appropriate adjustment or hold as needed.
For military use, many believe the 25m BSZ is ideal since at most normal combat ranges inside 300m, the soldier is either holding under to account for his trajectory, or pretty much center-mass, depending on the situation. In either instance, at no time is his front sight blade obscuring the target, as might occur when holding over.
If memory serves, army doctrine was to teach recruits to hold at the belt-line for most engagement ranges. Any present/former soldiers, feel free to correct that if needed….
The chief benefit of the Santose Improved Battlesight Zero is that it retains the capabilities of the legacy iron-sighting sighting system,while expanding its versatility inside 300 meters, the distance at which most people – especially civilians – expect to do their shooting. Most ranges are limited to 100, 50 or 25 yard distances, and at least in the U.S. are not graduated in meters (1 meter = 1.09 yards).
The Revised Improved Battlesight Zero system (RIBZ) simply takes the Santose system a bit further. It allows good 25, 50, 100 and 200 yard zeros, in addition to the normal use of the elevation wheel as before. But you will need a taller-than-stock front sight post for most 20-inch barrel rifles, as the standard post isn’t quite tall-enough.
For what it is worth, many Marines prefer the 36 yard near-zero as their everyday battle zero or maximum point-blank range setting. The Army, on the other hand, has stayed with its traditional 25m/300m system.
This debate is now somewhat academic – at least for the military – now that both the Army and Marine Corps have adopted optics as their standard-issue carbine/rifle sights. If there is any standardization to zeroing of BUIS in either of these two branches of service, I am unaware of it.
Given a decent exterior ballistics program and data for your load, i.e., bullet weight, muzzle velocity and ballistic coefficient, it is easy to dope out what the best maximum point-blank range or BSZ is for your particular set-up. Or, since few civilians – even cops – ever use a carbine for defensive purposes outside of fairly close ranges, put a 100 yard zero on it and call it done.
For non-tactical uses, use the normal hunter’s maximum point blank range method, which starts with the vital zone on the game animal in question and works backwards from that. If a coyote is assumed to be nine inches deep in the chest or brisket, that’s your vital zone. And so on.
Competitors in service rifle matches usually employ sights custom-made for this purpose, which allow precise, fine and repeatable adjustment at the appropriate ranges. White Oak Arms, Rock River Arms, etc. make these.
Herschel, with regard to your question about the heavier bullets now used by many folks, the simplest answer is to dope it out using a ballistics program and whatever data you can generate for your particular set-up. Each load has its own come-ups and particular trajectory characteristics. There’s no escaping having to do the grunt work at the range and in the field if you want to master your trajectory. But hey, the good news is that you are an engineer and have more capability with crunching numbers than most people out there…. so it ought to be a snap for you.
On October 16, 2021 at 5:07 am, Russell G. said:
“My complaint: He addresses only 55 grain bullets, and doesn’t seem to make much of barrel length. I’d like to see this thread expanded to include 68, 75 and 77 grains. A lot of guys are shooting heavier bullets now. That affects velocity, and thus changes everything.”
Xactly.
Get your chrono out for your load and your platform. And, don’t think your an idiot when you blow the top sun shades off…everyone does it at least once an outing.
You’ll need to burn up lots of rounds to get it dialed in. You just cannot copy and past a drop chart from someone else. You change that **specific** load for your platform (or any atmospheric variables for that matter) and you’re dope is bad. Not so much on a small 200ish yards, but the long shot won’t even be seen.
Also remember this. Boxed ammo powder is “blended” by lot (to get a velocity **average**), meaning that lot to lot differences will affect your drop chart. Take a look at any 3-4 cans of Accurate powders…notice that they are probably made in different countries. That’s why in the old days reloaders bought the powder in 8 lb jugs and only used that powder in one specific platform. Now, it’s merely hoarding IF you can even find powder.
On October 16, 2021 at 6:33 am, anon said:
I find this very helpful: https://store.appliedballisticsllc.com/product_p/dl2001.htm
ballistics engineer developed it.
On October 16, 2021 at 7:37 am, George said:
If you want to use an internet website try JBM Calculations-Trajectory.
Short yardage zeroes are a starting point. One must still verify the POI at the various yardages. Some do not have access to ranges with long distance berms. Therein lies the rub.
On October 16, 2021 at 5:46 pm, Georgiaboy61 said:
@ Russell
Re: “Get your chrono out for your load and your platform. And, don’t think your an idiot when you blow the top sun shades off…everyone does it at least once an outing.”
Even if not that, then struggling with an optical chronograph when lighting conditions are not ideal, or there is a stiff wind blowing. Get a Lab Radar doppler radar unit, you’ll be glad you did. Works rain or shine, or when the wind is blowing, and is also considerably more-accurate than most optical chronos. And no screens to shot through or under. The Lab Radar sits to the side of the shooter and his firearm, not downrange some distance.
It’s somewhat spendy for some people, at around $500, but suck it up and get it…. cry once, be happy thereafter.
On October 16, 2021 at 7:26 pm, JB said:
The irons on all my 5.56 AR’s are set at at a 36 yard zero. Im pushing 68 and these old eyes need corrective lenses to make good hits out to a 100 yards. I no longer hunt and so heavier loads are not in my SHTF stockpile which is limited to M193 and XM855 for the AR’s. I thank everone for providing useful information on this subject.
On October 17, 2021 at 12:23 pm, Tree Mike said:
Thanks so much. Best, most comprehensive, tables, info I’ve run across. Now do it for the 300 BO, please ( I know, 300yds is pushing it), or 308/7.62.
On October 17, 2021 at 4:52 pm, X said:
The rough rule of thumb from service rifle matches is:
Two to two, three to three, and twelve to six.
In other words:
From a 100 yard zero, two minutes elevation to 200 yards
From a 200 yard zero, three minutes elevation to 300 yards
From a 300 yard zero, 12 minutes elevation to 600 yards.
It’s not perfect but it’s “close enough” to get you “in the black.” Furthermore, this works with most service rifles regardless of caliber — 5.56, 7.62, 30-06.