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Posted: 3/25/2024 12:44:19 PM EDT
Looking for some guidance on this in general. I am beginning to understand that raising optics increases height over bore, and will alter a traditional zero (say the 50/200). Is there any resource that illustrates how much it's altered based on how much you elevate the optic?
First, I am looking at top mounting my RMR on my ACOG (currently offset). I saw delta thirty four's video on this where he breaks down the zero, which was very helpful. Looks like a 50/200 is now 50/263 (link below) I also have an Eotech on a Unity riser so I can use my nods comfortably. I have it zero'd at 50. Wondering how much this Unity riser will impact that zero the further out I go. It's not quite as high as an RMR on top of an ACOG but it's still elevated, so I wonder if my 50/200 is now more like a 50/240? https://www.youtube.com/watch?v=M33QOey2E0I |
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Posted: 3/25/2024 12:49:37 PM EDT
[#1]
Pretty much all ballistic calculators will factor in HOB, so you can use one of those to plug in your data and see how it will effect offsets from the primary zero distance.
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Posted: 3/25/2024 12:59:50 PM EDT
[Last Edit: piperpa24]
[#2]
The HAB is one part of computing a ballistic chart for a given ZERO (distance), beyond that it's about what height works for your particular rifle and optic setup.
If you're talking about open sights mounted right on the barrel the HAB is factor is fairly minimal. Here's an online ballistic calculator I've used a lot of the years, just to get rough ideas of different loads with different zeros. You can set the sight height with the advanced options, but it defaults to 1.5". http://gundata.org/ballistic-calculator/ |
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TX, USA
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Posted: 3/25/2024 1:14:48 PM EDT
[#3]
Just plug it in to a ballistic calculator. Been using Shooter and StrelokPro for years and I’ve found both to be very accurate.
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MN, USA
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Posted: 3/25/2024 1:19:24 PM EDT
[#4]
Quote HistoryOriginally Posted By D_Man: Pretty much all ballistic calculators will factor in HOB, so you can use one of those to plug in your data and see how it will effect offsets from the primary zero distance. This ^^^ You may find that a closer near zero will be required for a 200 yard far zero. Play with sight height and near zero distance until you get the downrange POI you seek. |
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SC, USA
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Posted: 3/25/2024 1:27:15 PM EDT
[#5]
The best free one is JBM Ballistics. Plug all of your information in on there, and it will give you what you need.
Use the trajectory page. |
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Posted: 3/25/2024 1:51:19 PM EDT
[#6]
I think HOB for their fast riser comes to 3.44 for ARs.
So, assuming you’re shooting xm193 going 3000fps, you’re looking at 50/250 yards. |
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Posted: 3/25/2024 1:58:21 PM EDT
[#7]
Like many have stated, calculators will get you where you want. Print out the results, laminate, and carry with you.
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Posted: 3/25/2024 2:06:23 PM EDT
[#8]
I have an XPS on an absolute riser on my 11.5”
Using a 3.48” HOB (2.26” + 1.215”) and M193 at 2818fps, a near zero of 50yd gives me a far zero of 243yd You’re going to have to use a ballistic calculator and a chronograph and just do the work. The information you get out of the calculator is only going to be as good as the data you input. |
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USA
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Posted: 3/25/2024 2:12:30 PM EDT
[Last Edit: 556NAT0]
[#9]
I actually cataloged this, it is on my desktop. The general trend is if all other factors (including zero distance) are the same, as your mechanical offset is increased closer shots shoot lower and further shots rise less over your optical axis (you don't have to hold lower). I settled on a 40yd zero utilizing a Unity mount on an 11.5", I factored in MPBR. I forgot my max drop/rise, but it probably wasn't more than 3". I figured 3" low at 5 yards is not a big deal, at longer distances I wanted the flatter trajectory.
Bear in mind, if we are comparing something like the Unity mount to a lower 1/3, the difference is less than 1 full inch. The differences are distinct, but not nearly as dramatic as many would have you believe. |
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Posted: 3/25/2024 2:36:46 PM EDT
[#10]
The ballistic calculators are a good place to play with numbers but just go shoot it to see how it all works out.
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Posted: 3/25/2024 7:05:24 PM EDT
[Last Edit: Molon]
[#11]
Quote HistoryOriginally Posted By 556NAT0: The general trend is if all other factors (including zero distance) are the same, as your mechanical offset is increased closer shots shoot lower and further shots rise less over your optical axis (you don't have to hold lower). False.  .... |
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Posted: 3/25/2024 8:05:22 PM EDT
[#12]
Quote HistoryOriginally Posted By Molon: False. https://i.ibb.co/MBzyDqX/trajectory-height-above-bore-comparison-001.jpg .... Quote HistoryOriginally Posted By Molon: Originally Posted By 556NAT0: The general trend is if all other factors (including zero distance) are the same, as your mechanical offset is increased closer shots shoot lower and further shots rise less over your optical axis (you don't have to hold lower). False. https://i.ibb.co/MBzyDqX/trajectory-height-above-bore-comparison-001.jpg .... Barrel lengths and zero variances can change the delta of the chart shown...but data is data |
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Posted: 3/25/2024 8:14:56 PM EDT
[#13]
The best thing you can do is go out and shoot to see where it hits.
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Posted: 3/25/2024 8:25:32 PM EDT
[#14]
Quote HistoryOriginally Posted By DefenderAO: Barrel lengths and zero variances can change the delta of the chart shown...but data is data Quote HistoryOriginally Posted By DefenderAO: Originally Posted By Molon: Originally Posted By 556NAT0: The general trend is if all other factors (including zero distance) are the same, as your mechanical offset is increased closer shots shoot lower and further shots rise less over your optical axis (you don't have to hold lower). False. https://i.ibb.co/MBzyDqX/trajectory-height-above-bore-comparison-001.jpg .... Barrel lengths and zero variances can change the delta of the chart shown...but data is data But this was predicated on everything else being equal except HOB. Barrel length and zero distance shouldn’t affect the equation. Am I missing something? |
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Posted: 3/25/2024 9:12:20 PM EDT
[#15]
Quote HistoryOriginally Posted By Luny421: But this was predicated on everything else being equal except HOB. Barrel length and zero distance shouldn’t affect the equation. Am I missing something? Quote HistoryOriginally Posted By Luny421: But this was predicated on everything else being equal except HOB. Barrel length and zero distance shouldn’t affect the equation. Am I missing something? No you're not missing anything. Originally Posted By 556NAT0: The general trend is if all other factors (including zero distance) are the same, as your mechanical offset is increased . . . |
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Posted: 3/25/2024 9:34:56 PM EDT
[#16]
when I added risers to my stuff, I played with zero's online with new HOB. I came to find the 75 was the sweet spot.
the 50yd zero with exps on unity riser was all over the place, according to my calculations with a 12.5 with proper FPS of 193's from a 12.5... 50yard zero: -3.4" at 0 yds 0 at 50 +1.25 at 75 +3 at 140 +2.9 at 175 0 at 240/250 75 yard zero: -3.4 at 0yds -.84 at 50yds 0 at 75 +.67 at 140 0 at 175 -3.4 at 240/250 the 75yd zero made more sense on paper, less large swings up + and - . from 50yds to 200yds, your either .7 low or high. not a 3" high peak . more of a dead hold on target, more "flat" zero... i have no confirmed past 100yds, but 100yds, it seems to match up with the vortex ballistic calculator online. |
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USA
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Posted: 3/26/2024 4:42:46 PM EDT
[Last Edit: 556NAT0]
[#17]
Quote HistoryOriginally Posted By Molon: False. https://i.ibb.co/MBzyDqX/trajectory-height-above-bore-comparison-001.jpg .... I did make a mistake saying zero distance, I admit that my memory failed me or I wasn't careful enough with the words selected. But I believe your data is missing the duplicate MPBR I indicated earlier. I will certainly re-run my numbers, but I'd advise trying it again with the same MPBR. |
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IN, USA
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Posted: 3/26/2024 9:56:02 PM EDT
[#18]
You mentioned Delta34. Hope you also saw this one.
 MUZZLE awareness, and HEIGHT over BORE professionalism. Jbm simplified trajectory is a good start as previously mentioned. |
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Posted: 3/29/2024 11:58:59 AM EDT
[#19]
For what it's worth, I work for UNITY Tactical. Here is a ballistics chart comparing FAST height to lower 1/3 and absolute cowitness height optics out to 500 yards (max point target effective range of the M4 according to the US Army). Data is for a 50 yard zero.
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USA
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Posted: 3/29/2024 12:34:44 PM EDT
[Last Edit: 10-8DoWork]
[#20]
Ultimately comes down to ammo, barrel length, and you, but I've found that on shorties (10.5-12.5) a 100yd zero is the easiest for me to manage holds.
Traditional 25 and 50yd zeros forced a "hold under" at certain distances which I didn't care for. It wasn't intuitive. YMMV |
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VA, USA
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Posted: 4/1/2024 6:09:27 PM EDT
[#21]
Its more often called 'sightline' and since it is always inclined relative to the bore, you always measure it at the chamber. It is the most important factor in sighting because it is the constant upon which all else depends. A difference in the sightline obviously will affect the elevation of the trajectory at all points but it has to be severe to be a factor in the range of the far zero. The far zero in casual or 'combat' shooting is pretty variable anyway because of all the different kinds of ammo you can use, weather conditions, etc., so I'd say if you can manage to hit a B9 torso target anywhere at your far zero, you're good. You should still zero at 50m. You could check in at 100 mainly for windage correction on a calm day, but you could note the trajectory at 100 for comparison to the theoretical trajectory if you wish, but they both will be high.
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