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Posted: 2/12/2011 5:02:25 PM EDT
[edit, title updated per suggestion. Some updates and additional calculations to be performed soon. Will produce a similar graphic for IMI 62 gr M885 ammunition, and some tables of numerical values as requested].
It's a common question, and one I'm revisiting. After two hours of analysis with a ballistics calculator, I decided to share my own personal assessment. Your goals and applications may be different - there is no One Correct Answer. Scenario: RRA 1/9 16" Middy with an EOTech XPS2-0 mounted on a LT-110, for a sight hight of ~ 2.875" Ammunition: Handholds to simulate M193: 55gr Hornady FMJBT, 28.0gr BLC2, 2950 fps muzzle velocity* (*Technically M193 should have 3132 FPS out of a 16" barrel, though I've never seen this.) Conditions: 1150' elevation, 32 °F local temperature. A spectrum of zero distances were considered: 25, 50, 75, 90, 100, & 200 yards My goal was to have a relatively flat profile. I also wanted my zero to be within about an inch at 100 yards. Trajectory was only considered out to 200 yards. I know many prefer to assess a 300 yard trajectory, but for a light carbine with a holosight, I do not. Each of the zero distances were entered into the Android ballistics calculator "Shooter", which was used to model trajectory. Results are shown in the below graphic. 
Discussion: The 25 yard zero and the 300 yard zero's both were rejected. >4" high at 100 yards was not acceptable to me. The 25 yard zero was particularly interesting. My thought was it would be a good close quarters/indoors zero (i.e. <15 yards). It didn't really shine. For indoor work (<10 yards), it's still about as off as the others, at 2" or so. At 100 yards it's ridiculously off. I finally concluded that trying to get a good zero that also worked indoors really wasn't practical. The 50 yard zero was also rejected. Too high over the range spectrum. The 200 yard zero was getting closer, but was rejected because it was greater than 1" high at 100 yards. Read below, because it ends up really close to what I selected. I like the 75 yard zero. It's about 1.5" low at 25 yards (no worse than most), 0.5" high at 100 yards, and only 1.5" low at 200 yards. The 100 yard zero is interesting too. It's your classic zero, because that's what most ranges offer for rifles. Interestingly, it is also the peak of the arc. If you zero the AR for 100 yards, it'll never traverse above zero. Whereas most other zero distances will yield a trajectory where the bullet will hit higher than the zero at some yardages. If you think about it, unless all shots are for sure going to be at 100 yards, this says a 100 yard zero isn't that great. Let's assume 1" of play is acceptable. If that's the case, you should select a zero such that a wide spectrum is +/- 1" from zero. A 100 yard zero will have a less generous range of that, because it never goes into the +1" zone. Or in other words, it'll always shoot low unless you're spot on at 100 yards, and have a smaller yardage range where it's hitting within 1" of center. Indeed, this is why the 75 yard zero was pretty attractive to me. The 90 yard zero was essentially the same as the 100 yard zero. Conclusion: The 200 yard zero is close to what I will select. Actually, I'm going to zero the rifle such that it is shooting ~1" high at 100 yards, which is a 60 yard zero. This will have a very flat trajectory out to 200 yards. Theoretically that will hit 0 at 60 and 195 yards. It will be 1" high at 100 yards, and the apex of 1.3" will be reached at 130 yards. At 200 yards it will be 0.3" low, and be within 2 MOA of zero out to 260 yards. Note I said theoretically, because the error of a group from a 16" lightweight Middy is such, that it will be extremely difficult to be certain that this 1.5MOA rifle is zero'd to 1" +/- 10% at 100 yards anyway. In practice, zeroing the rifle, to be a "lil high, maybe an inch" at 100 yards. Additional commentary: If serious about indoor use, I suspect one is better served with a laser sight mounted closer to the bore axis than a heads-up holographic sight. But considering most indoor encounters, I'm guessing shooting 3" low really isn't a big deal. |
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Posted: 2/12/2011 9:43:01 PM EDT
[#1]
Interesting stuff. Thanks for sharing
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Posted: 2/13/2011 5:19:24 AM EDT
[#2]
 Will revisit once brain has caught up with the coffee. Thanks for sharing.
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Posted: 2/13/2011 6:23:17 AM EDT
[#3]
Thanks for posting.
My black rifles mostly ride along with me in a Rhino. I might be shooting at a crow 400 yards away, and at a water mocassin at my feet, all within a few minutes. With my rifle sighted in at the normal 50 yd sight-in, I have a better chance at 400 yards than the snake. I dunno, to me its hard to do the mental math necessary to compensate for the sight height for something up close. (especially a target that bites you if you aren't quick) I've considered and used a laser pointer, but generally wind up going back to something more basic, just cause I have to turn it on. |
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Posted: 2/13/2011 7:33:21 AM EDT
[#4]
Will the graph go out to 300 yards?
Posted Via AR15.Com Mobile |
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Posted: 2/13/2011 10:17:13 AM EDT
[#5]
Here's the same analysis, but with M193, in the form of CCI Lawman ammunition. Muzzle velocity from my 16" rifle is 3042 FPS. I changed the conditions to be 600' elevation and 81 °F (i.e. Camp Perry conditions). In this case, I ran it out to 300 yards in the graph, as requested.
If 300 yards is your range of interest, then a 50 yard zero looks about the best if you don't want to adjust sights for elevation. Personally, I am less interested in holding zero out to 300 yards, and will still stick with the 60 yard zero (which also equals the 200 yard zero). The 3" high arc of the 50 yard zero bugs me. |
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Posted: 2/13/2011 11:11:47 AM EDT
[#6]
Thank you for the graph to three hundred . I'm thinking about the same zero as you I just like to seee were the bullet is headed after 200 yards. I need to invest in some software. I have programs on my phone but its too small to work on for me.
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Posted: 2/13/2011 2:11:31 PM EDT
[#7]
Another way to look at it - the 60 yard zero keeps you within 1" of dead on for about a 200 yard span. None of the others hold so close. That's why I like it.
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Posted: 2/13/2011 2:18:31 PM EDT
[#8]
Do you mind posting the POI in inches at 25 yards? It seems to be about -2 inches for most of the trajectories. Thanks.
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Posted: 2/14/2011 6:25:01 AM EDT
[#9]
How much would this differ with a heavier bullet, say 62gr?
Thanks |
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Posted: 2/14/2011 7:07:08 AM EDT
[#10]
Quoted:
How much would this differ with a heavier bullet, say 62gr? Thanks Not a lot, more so at longer ranges. Plan on running those calculations in full in a few days. |
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Posted: 2/14/2011 7:56:01 AM EDT
[#11]
Thanks a lot for posting this article. It's always nice to see some independent thought being displayed. I have a couple of suggestions:
Take the "EOtech" out of your title - it's largely irrelevant to the subject being discussed, although I understand that sight height plays an important part. Also refer to the post by Sylvan covered under the Optics FAQ entry #7. There was a pretty good discussion that basically went through what you have posted, and Sylvan came up with some compelling reasons to use the 100 yard zero. I'll probably fire up my own ballistics program and do something similar to what you've done to create an extra FAQ entry. I'll just create charts of all different zeros for people to peruse and the tabular data that spawned it. What you have done basically covered it, so I'll give you credit. Thanks again... |
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Posted: 2/16/2011 8:42:29 PM EDT
[#12]
Thanks. I'll incorporate these suggestions. Busy work schedule. I collected some additional velocity data at the range, and will update as soon as able.
Not surprisingly, it was difficult to get a confident 1" high group using just an EOTech without a magnifier at 100 yards. Better approach was to place a target at 60 yards using a laser range finder. Ideal approach will be a 60 yard target and have a Magnifier (my magnifier mount is delayed in shipment somewhere). Using 10 shot groups and average center, fire 3 groups to get centered at that yardage. I read Sylvan analysis per your suggestion, and agree with his premise. Though for me, I still prefer a 60 yard zero. 1.3" high at the Apex is a very minor degree of high. Others obviously will have different opinions. |
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Posted: 2/17/2011 7:11:26 AM EDT
[#13]
Agreed. It's nice to see the actual trajectories as it gives people a better idea what impact zeroing distance has on bullet impact. That gives them more knowledge to make an informed decision. Thanks again for your work.
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Posted: 2/18/2011 2:16:12 PM EDT
[#14]
Here is the trajectory spectrum for IMI 62 gr ball. The muzzle velocity indicated was measured from a 16" RRA lightweight middy barrel 1/9 chrome lined. Ammo was at 32 °F, so rather cool. Possible velocity of warmer ammo will be higher, but should be good enough. Calculator was used at 1150' elevation, 65 °F, 75% Relative Humidity.
Data in 5 yd increments to 600 yards available in Excel if anyone wishes to volunteer hosting it. |
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Posted: 2/18/2011 4:26:13 PM EDT
[#15]
testing if this works. Attached is the Excel file with the numerical predictions.
http://www.mediafire.com/?j2e671ezvt0thx2 |
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Posted: 2/18/2011 4:49:05 PM EDT
[#16]
Here's my take on it. I used a 55gr Hornady FMJ at a muzzle velocity of 3080fps, AR15 sight height of 2.6" (same as iron sights and cowitnesses red dots and such). First is the 400 yard range trajectory:
 Zoomed in on the 200yard range:  And finally, the raw data in PDF form: http://www.ar15.com/media/viewFile.html?i=26756 Range 25yd 37.5yd 50yd 67.5yd 75yd 100yd 150yd 200yd 250yd 300yd Velocity |
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Posted: 2/20/2011 4:53:36 AM EDT
[#17]
Quoted:
Agreed. It's nice to see the actual trajectories as it gives people a better idea what impact zeroing distance has on bullet impact. That gives them more knowledge to make an informed decision. Thanks again for your work. I can't believe you of all people allowed an actual technical discussion to run in the tech forums. What is this place coming too? 
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Posted: 2/20/2011 6:58:42 AM EDT
[#18]
any chance one of you guys could run a calculation on 62 bonded fed tactical out of a 10.5 inch barrel? - I apologize but I do not have MV values - will try to get though next time I head out to the range.
Mark |
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Posted: 2/20/2011 7:07:58 AM EDT
[#19]
Quoted:
any chance one of you guys could run a calculation on 62 bonded fed tactical out of a 10.5 inch barrel? - I apologize but I do not have MV values - will try to get though next time I head out to the range. Mark The primary impact that the barrel has on the external ballistics is from the muzzle velocity. So without that data, there is little that can be done. (For extreme ranges, twist rate starts to play a roll too, but that's not really going to apply to a 10.5" bbl). |
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Posted: 2/20/2011 5:53:13 PM EDT
[#20]
Quoted: any chance one of you guys could run a calculation on 62 bonded fed tactical out of a 10.5 inch barrel? - I apologize but I do not have MV values - will try to get though next time I head out to the range. Mark http://www.handloads.com/calc/ |
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