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Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic #8002619 10/08/20 03:03 PM
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I’ve long wondered but haven’t ever tested whether optic technology has a significant effect on Point of AIM and Point of Impact at distance.

Usually night time hunting engagements are 200 yards or closer which doesn’t amount to much “drop” in center fire rifles.

However this can be skewed heavily dependent on caliber and velocity and so my question is - has anybody done the testing or have a resource to read on A versus B ?

A represents a specific rifle and ammo config - zeroed at 100 yards and then fired at 50 / 100 / 150 / 200 / 300 yards with a traditional scope

B represents same rifle and ammo zeroed at 100 yards with a thermal or digital optic and fired at the same ranges.

I can recall many times when the drop data for factory loads doesn’t match up with thermal or digital optics - not even close really...

What causes the difference in drop between the two optic types - if it is proven to be different ?


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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: Pig_Popper] #8002623 10/08/20 03:10 PM
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Bullet drop will be affected by velocity, weight of the bullet, BC, and gravity. It will not matter what optic you have on the rifle as the optic does not affect drop.


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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: Pig_Popper] #8002632 10/08/20 03:20 PM
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Im not 100% sure of the question. If the two optics have different mounting heights it could change your corrections given the same rifle/ammo.


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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: Pig_Popper] #8002678 10/08/20 04:03 PM
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To state it simply:

The box of ammo or the website says - drop at 50/ 100 / 200 / 300 / 400 etc is x inches

That data is based on traditional optics 100% of the time and using 24” barrel (usually).

MOST times users are within an inch of that using 20, 22, 24” guns and traditional optics.

Does this translate to thermal and digital optics ?

My experience tells me - no but I’ve yet to test and prove or disprove my therory.

Asking others who hunt thermal and digital if once you zero at 100 do you see a great shift at 200 + yards with thermal / digital versus traditional optics....


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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: Pig_Popper] #8002684 10/08/20 04:10 PM
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Right, so the thing with thermals is that often their sight height is higher than traditional optics and that throws thingsvoff from the manufacturer's drop approximations.


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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: unclebubba] #8002755 10/08/20 05:24 PM
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Originally Posted by unclebubba
Bullet drop will be affected by velocity, weight of the bullet, BC, and gravity. It will not matter what optic you have on the rifle as the optic does not affect drop.


^^^^ this


Originally Posted by Phil Robertson
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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: Judd] #8002776 10/08/20 05:46 PM
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Originally Posted by Judd
Originally Posted by unclebubba
Bullet drop will be affected by velocity, weight of the bullet, BC, and gravity. It will not matter what optic you have on the rifle as the optic does not affect drop.


^^^^ this


And is there anyway then to offset this ?

I don’t read on any aftermarket mounts that the condition can be normalized ...

I think one of the thermals I have is a low height scope and it shifts a good deal while my traditional optic is in high rings ...

I’ll be sure to add this information to my testing process

Thanks


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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: unclebubba] #8002854 10/08/20 06:35 PM
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Originally Posted by unclebubba
Bullet drop will be affected by velocity, weight of the bullet, BC, and gravity. It will not matter what optic you have on the rifle as the optic does not affect drop.

And the environmental conditions like temperature, humidity, air density, etc. Of course those are pretty minimal at the ranges the OP mentioned, but when you're shooting 1000+ yards you better be paying attention.

And I think as others have mentioned, the mounting height of the optics may be what's skewing the numbers. Most night vision optics mount way higher than traditional rifle scopes.


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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: Pig_Popper] #8002930 10/08/20 07:43 PM
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CTR, 143 gr ELDX, 1.5" sight height, 2790fps:
100 - 0
150 - -1.0"
200 - -3.4"
250 - -7.0"

Same, 2.25" sight height:
100 - 0
150 - -.7"
200 - -2.6"
250 - -5.9"

I agree with others, it's the difference in height. Other than that there should be no difference.


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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: Double Naught Spy] #8002983 10/08/20 08:09 PM
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Originally Posted by unclebubba
Bullet drop will be affected by velocity, weight of the bullet, BC, and gravity. It will not matter what optic you have on the rifle as the optic does not affect drop.



Originally Posted by Double Naught Spy
Right, so the thing with thermals is that often their sight height is higher than traditional optics and that throws thingsvoff from the manufacturer's drop approximations.


This and this. The bullet drop does not change at all if it's the same rifle and same ammo being shot. How the optic it mounted, and the quality of the image to make a precise shot will effect the POI. I know some lower end thermals it is difficult to shoot a tight group with, and therefore it is difficult to be exact with shot placement. That would effect the the POI. And most thermals have a scope height of about 3" to 3.5". That will make the most difference, especially at close range.



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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: Pig_Popper] #8003030 10/08/20 08:42 PM
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Good points Chad

Yes this question is mostly about how the scope changes the POI and by how much.

I’ll report back after doing some shooting and logging on results


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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: Pig_Popper] #8003074 10/08/20 09:16 PM
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Good explanation and graphics for bore height and bore center and scope centerline

Granted he is talking pellet (air rifle) but same principals apply.

Let me go measure some scope height distances


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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: Pig_Popper] #8003803 10/09/20 02:23 PM
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Run the trajectory data on your ammo with the exact scope height with the proper zero you are running. The data you enter must be exact with your zero. Everything stems from a proper rifle zero. "Close" doesn't always work for a zero, which I know many shooters who like to be just "close"



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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: Pig_Popper] #8003822 10/09/20 02:33 PM
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Here's something else to consider. The difference from a 50 yard zero to a 100 yard zero with a thermal that has a 3" scope height is pretty big. A 50 yard zero will get you closer to line of sight under about 75 yards. But after 75 yards, the bullet path is still in an upward trajectory, and you hit high on anything past 100 yards on normal shooting distances (80 to 150 yards). With a 100 yard zero, the POI is closer to the line of sight from about 60 yards out to about 180 yards. You are within 1" from those distances. I know many shooters who zero their thermals at 50, but have problems with making good hits on critters because of the POI difference that a 50 yard zero offers. I ran these numbers with a 224 Valkrie and 75 grain bullet, which is what I use for my thermal hunting currently.


3" scope height, 100 yard zero
Range Elev Velocity Energy
(yards) (inches) (ft/sec) (ft-lbs)
0 --- 2900 1400.5
20 -2.05 2861.9 1363.9
40 -1.27 2824.2 1328.2
60 -0.67 2786.7 1293.2
80 -0.24 2749.6 1259
100 0 2712.9 1225.6
120 0.05 2676.4 1192.8
140 -0.09 2640.3 1160.8
160 -0.43 2604.4 1129.5
180 -0.98 2568.9 1098.9
200 -1.73 2533.7 1069
220 -2.71 2498.7 1039.7
240 -3.9 2464.1 1011.1
260 -5.33 2429.8 983.2
280 -6.99 2395.8 955.8
300 -8.89 2362.1 929.1

3" scope height, 50 yard zero
Range Elev Velocity Energy
(yards) (inches) (ft/sec) (ft-lbs)
0 --- 2900 1400.5
20 -1.67 2861.9 1363.9
40 -0.51 2824.2 1328.2
60 0.47 2786.7 1293.2
80 1.27 2749.6 1259
100 1.89 2712.9 1225.6
120 2.32 2676.4 1192.8
140 2.56 2640.2 1160.8
160 2.6 2604.4 1129.5
180 2.43 2568.9 1098.9
200 2.06 2533.7 1069
220 1.46 2498.7 1039.7
240 0.64 2464.1 1011.1
260 -0.4 2429.8 983.2
280 -1.68 2395.8 955.8
300 -3.21 2362.1 929.1



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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: Pig_Popper] #8004595 10/10/20 01:12 AM
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What website can I use to plug in data and get an output like that ?

Today I almost had some good test results to share and then Murphy butted in...


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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: Pig_Popper] #8004642 10/10/20 01:48 AM
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jbmballistics.com

I’ve also heard very positive things about the Hornady app on the phone. I use shooter and it’s good but there is a fee.


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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: Pig_Popper] #8005044 10/10/20 04:10 PM
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I use this one, which is also JBM data.

http://www.mega.nu:8080/traj_dat.html



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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: Pig_Popper] #8005065 10/10/20 04:34 PM
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Re: Do points of impacts (drop) DIFFER for a specific rifle and load when using traditional optics versus thermal / digital optic [Re: Pig_Popper] #8005156 10/10/20 06:04 PM
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So here is the first set of targets - I’ll admit upfront this information is useless , read below

Calm conditions , rifle bagged front and rear , shooter mostly comfortable .

308 Winchester - Sellier Belot 150 grain sp ammo.

LEUPOLD 8.5-25x56mm w target dot reticle - I ordinarily use this scope for all my load development , I had one screw head starting to strip so didn’t lock it on the rail as tight and even as I’d like - I know I know - WHY BOTHER....

[Linked Image]

Despite my best intentions to zero EXACT at 100 yards (to Chad’s earlier point) it just wasn’t in the cards. I was just chasing impacts going nowhere fast so i said screw it - an 1” low at 100 it is....

Green circles indicate groups at 200 and 300 yards

Scope height above bore centerline is 3.0”

50 yards : 2 inches low
100 yards : 1 inch low
200 yards : 4.5 inches low
300 yards : 15.5 inches low

Ok so with the traditional optic out of the way and time becoming an issue for my range visit I decided to skip the thermal scope test and went with a digital day/night scope that has recording capability onboard with audio.

SIGHTMARK WRAITH 4K - 3-24x50mm with a fine aim dot reticle. This scope needs to be mounted far back on the top rail for best eye relief , so I’m speculating that the rail pressure is a bit uneven due to the contour of the ar15 top rail towards the charging handle. Anyhow 10 out of 10 times I am mounting the scope at this location due to best eye relief.

[Linked Image]

With this optic I find that I can shoot very week therefore the zero is EXACT at 100 yards

Green circles indicate groups at 200 and 300 yards

Scope height above bore centerline is 2.75” (nearly the same as the Leupold)

50 yards : .5 inches low
100 yards : 0.0
200 yards : 2 inches low
300 yards : 10.5 inches low

So I was sorta shocked at the variance due to the scopes only being a 1/4 difference in rail height - hence back to my theory on different technologies of scope ALSO being a factor BUT with the non-exact zero of the Leupold I guess I can’t prove myself right or wrong...

I still want to try a thermal scope , it sits even lower on the rail than these two but I’m pretty sure the drop is just as much .....

Last edited by Pig_Popper; 10/10/20 07:11 PM.

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