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Posted: 4/4/2006 6:39:02 PM EDT
[Last Edit: 4/5/2006 3:58:43 AM EDT by ABNAK]
I have an Armalite AR10 with a 20" barrel and flattop upper. I have a TA11C ACOG for it. I know that the TA11C is made for a carry handle mount, but the ACOG FAQ says that if I sight it in 0.7" high at 100 yards (meters?) on a flattop that all the ranging marks will be within 0.5" out to 600. Pretty damn close for me. According to Trijicon, the TA11C is calibrated using 168gr BH at a muzzle velocity of 2500 fps. I forgot to ask what the height above bore is that they use with the carry handle, or if it is in yards or meters.

Okay, this is where it gets difficult: I want to use M80 Ball or equivalent (Winchester white box, South African, or any kind of 7.62 NATO 147-150gr FMJ) to sight in my ACOG, as I can't afford a steady diet of Black Hills 168gr Match ammo. I know that the NATO type, 147-150gr stuff will have some variances, but they should all be in the ballpark of each other minute-of-ACOG-wise. Having all the data from Trijicon except the height over bore and the yards/meters thing for the 168gr BH, I want to figure out what my drops and holdovers from the etched lines on the ACOG will be for the NATO FMJ stuff.

Obviously the reticle can still be used for rangefinding, but I am assuming I'll need to know what the drop in inches at the various ranges will be for 168gr BH (hence the hashmarks), and then compare to the drop in inches for the NATO FMJ rounds. In other words, if the stadia line indicates a target at 500 yards (meters) on the TA11C then how far under/over the established stadia line should I hold for the NATO FMJ ammo?

The missing parts of the equation are the yards/meters measurement and the height over bore measurements for the carry handle and the flattop. Or will they even matter? I'm thinking that if I use the data and sight-in point of aim (top of the donut at 100 whatever) with the NATO stuff then all I need to know is the drops at the various ranges of the BH 168gr to guesstimate holdovers/under.

Hope this isn't too confusing....
Link Posted: 4/4/2006 7:59:53 PM EDT
I have the same ACOG but no idea how to figure that out. I have mine dialed in for 100yrds with SA308 surplus. I don't think the difference should be that great but then again I am no expert.

I would IM NewARGuy. He has the same setup as you I believe. He seems to know a lot about the TA11C. Just check out his avitar.
Link Posted: 4/5/2006 4:03:48 AM EDT
Well I know, for instance, that the NATO FMJ rounds tend to shoot several inches lower at 100 yards than the BH 168gr. Eventually I would imagine their paths intersect---or maybe not. The difference in their respective paths over the distances is probably what I need to know.

Anyone got a ballistics calculator????
Link Posted: 4/5/2006 5:40:34 AM EDT
[Last Edit: 4/5/2006 5:41:25 AM EDT by bjwar10]
IMHO the easiest way to get the info you are looking for is go to the range and do some shooting. Trying to make a ballistics chart from a different chart based on a different round from a different rifle is not much better than guess work.


BTW - Zak Smith is going to be your best bet when it comes to existing charts etc. and IIRC he is a big fan of the TA11.
Link Posted: 4/5/2006 6:12:33 AM EDT
Height over bore is around 3.6" on a carry handle mounted ACOG. 109yds = 100m.

Generally, you will hit within the illuminated portion of the reticle out to 300m without having to figure out different ballistics; past that it pays to know the difference.
Link Posted: 4/5/2006 7:31:04 AM EDT

Originally Posted By Bartholomew_Roberts:
Height over bore is around 3.6" on a carry handle mounted ACOG. 109yds = 100m.

Generally, you will hit within the illuminated portion of the reticle out to 300m without having to figure out different ballistics; past that it pays to know the difference.




Yeah, I kinda figured that the longer distances is where the "rubber meets the road". Unfortunately around here a 400, 500, or 600 meter range is non-existant. That kinda rules out actually shooting the rounds for measurement. I'll have to calculate as best as possible.

What I was hoping to be able to do is overlay the bullet paths of each load and determine the differences at each various range.

Example (these are made-up measurements for the sake of discussion): My ACOG ranging stadia line tells me the target is approximately 500 meters away. I know that the 168gr round drops 44" at that range, so the 500m stadia line accounts for a drop of 44". However, the NATO FMJ loads drop 60" at that range. I then know that I need to hold the 500m stadia line @ 16" higher for a torso-sized shot, maybe up around the neck area for a center-of-mass hit. See where I'm going with this?
Link Posted: 4/5/2006 7:31:48 AM EDT
Link Posted: 4/5/2006 11:23:32 AM EDT

My ACOG ranging stadia line tells me the target is approximately 500 meters away. I know that the 168gr round drops 44" at that range, so the 500m stadia line accounts for a drop of 44". However, the NATO FMJ loads drop 60" at that range. I then know that I need to hold the 500m stadia line @ 16" higher for a torso-sized shot, maybe up around the neck area for a center-of-mass hit. See where I'm going with this?


O I definitely see where you are going with it... I did just that for the link Forest mentioned, though I may not have the data you need there. Just keep in mind that you are comparing two parabolas and that there isn't a constant distance between them at all ranges. There might be a 22" difference at 400m and a 9" difference at 500m (figures are imaginary and just to illustrate the point).
Link Posted: 4/5/2006 5:45:22 PM EDT

Originally Posted By Bartholomew_Roberts:

My ACOG ranging stadia line tells me the target is approximately 500 meters away. I know that the 168gr round drops 44" at that range, so the 500m stadia line accounts for a drop of 44". However, the NATO FMJ loads drop 60" at that range. I then know that I need to hold the 500m stadia line @ 16" higher for a torso-sized shot, maybe up around the neck area for a center-of-mass hit. See where I'm going with this?


O I definitely see where you are going with it... I did just that for the link Forest mentioned, though I may not have the data you need there. Just keep in mind that you are comparing two parabolas and that there isn't a constant distance between them at all ranges. There might be a 22" difference at 400m and a 9" difference at 500m (figures are imaginary and just to illustrate the point).




Oh I know there will be a difference in the trajectories over distance, I was just going to write them down and memorize them. Kinda like a REAL sniper knows the "dope" on his rifle and scope. I would only have an interest in memorizing out to, say, 600 (or 700 max) meters. If the donut part of the reticle as is will pretty much cover things out to 300, then I only have to memorize the 400, 500, and 600 meter holdovers for a total of 3 to remember. Accuracy beyond 600 meters with M80 Ball equivalents is not optimal (doubly so with my shooting).


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