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Posted: 10/9/2009 7:21:48 AM EDT
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Hi all,
Can someone educate me or link me to a good technical overview of ACOGs; I'm not talking about the usual "technical brochure" type of info but rather all the other stuff I need to know to really understand the workings of ACOGs from a practical perspective. For instance, how are these things sighted in, at what range, and why? What if I want a 200m zero, or a 300m zero? Is the bullet drop compensation accurate only for certain combinations of scope/barrel spacings and ammunition? The spacing between the barrel and scope will affect the sighted-in trajectory and bullet drop; type of ammunition will affect this as well, and I don't see how a fixed drop compensator within the scope can be accurate for all combinations of rifles/ammunition. The sight-in range also has a big affect on bullet drop. Is the bullet drop compensation accurate only for a particular sight-in range? If so, what range, and why? I looked at the BDC thread but it leaves a lot of questions in my mind. I don't like doing things from instructions without understanding the why's behind them, especially when spending large $$. Basically I need the inside technical scoop on these scopes from anyone who is an expert or at least knowledgeable and experienced enough to contribute some good, practical technical info. Much appreciated! Thanks, Jimmy |
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Right at the top of this section are tacked threads with the answers to all your questions.
http://www.ar15.com/forums/topic.html?b=3&f=18&t=229420 Amazing, ain't it?!! |
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Right at the top of this section are tacked threads with the answers to all your questions. http://www.ar15.com/forums/topic.html?b=3&f=18&t=229420 Amazing, ain't it?!! You are not understanding my question and have obviously not taken the time to fully read my post. I stated originally that I looked at the BDC post that you so sarcastically pointed out. The BDC post is very good at explaining *what* to do, but is light on explaining *why*. If you are happy with having an incomplete knowledge of the ACOG and relying blindly on someone else to tell you how to use it then so be it. For me, this is not sufficient. I will give just one example below, not that I expect you to have taken the time to read this far: the BDC post states the following: "5.56mm Carry-Handle BDCs All full size ACOGs for 5.56mm use this BDC with the exceptions noted below. It is designed around a 20" barrel firing M193 with the ACOG mounted in the carry handle. If you have one sight in according to your manual." "For a Flattop 16" firing M193: Sight in 1" high at 100m. You'll be 0.3" high at 200, 0.7" low at 300 and within MOA until 600 where you will be 10" low." Okay fine. So it *sounds* like the ACOG is designed to operate on top of the carry handle with a 20 inch barrel firing M193. Assuming this is true, which carry handle are we talking about: fixed or removable? Most fixed handles are 2.8 inches above the barrel, whereas most removable handles are 2.6 inches above the barrel. This makes an non-trivial difference in the trajectory. There's just one question I have. There are many more. I'm sure there are experienced ACOG users who will get what I'm asking about here and can fill me in, unlike yourself. JH |
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A lot depends on exactly what type of ACOG you're interested in. BDCs, mouting options, ballistics, etc. are dependant on the model.
I still say all your answers are either in tacked threads or the ammo oracle, or can easily be found in 5 minutes by googling something like "m193 barrel length muzzle velocity" or somesuch. But I guess I'm just too sarcastic and reading disabled to be able to provide you of any real assistance. |
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for a given ACOG is there an easy way to see what parameters (scope height, ammo, etc.) it is designed for? JH JH, like you we would find such information invaluable, however it doesn't exist in a given place. And with the dizzying array of models offered now, it would be even more helpful. Fortunately Trijicon is generally very responsive to releasing such info if requested by phone call or email. I was told that they do offer many more BDC reticles than are advertised on their website, but essentially all of these aren't suitable for rifles, but crew served weapons. Searching these forums, checking the above BR ACOG chart, or posting a direct question wil give you most of the info you may need. For instance, the TA11C is set up for a carry handle mount rifle (3.5") shooting 168gr .308 ammo at 2500fps with a BC of .447. The TA55A is 175gr .308 with BC .505 at 2651fps with sight height of 2.7". The TA31F is 62gr M855 with BC of .304 @2970fps with a flat top mount (2.5"). The best option is spending some time with this data and then working with it in a ballistics program to seewhat the result will be on modifying the zero. Then, the real fun begins when you g to the range to try to verify your calc. |
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JH, like you we would find such information invaluable, however it doesn't exist in a given place. And with the dizzying array of models offered now, it would be even more helpful. Fortunately Trijicon is generally very responsive to releasing such info if requested by phone call or email. I was told that they do offer many more BDC reticles than are advertised on their website, but essentially all of these aren't suitable for rifles, but crew served weapons. Searching these forums, checking the above BR ACOG chart, or posting a direct question wil give you most of the info you may need. For instance, the TA11C is set up for a carry handle mount rifle (3.5") shooting 168gr .308 ammo at 2500fps with a BC of .447. The TA55A is 175gr .308 with BC .505 at 2651fps with sight height of 2.7". The TA31F is 62gr M855 with BC of .304 @2970fps with a flat top mount (2.5"). The best option is spending some time with this data and then working with it in a ballistics program to seewhat the result will be on modifying the zero. Then, the real fun begins when you g to the range to try to verify your calc. Yeah this is pretty hairy because even if I take an ACOG and make "adjustments" for my particular setup, the BDC could still be off. What I mean is depending on given parameters, I believe the distance between the 400 & 600 lines on the BDC hairs in the reticle could be different. I might make adjustments so the 400 line is on, but then the 600 line could be off, unlless I go with the recommended or default setup. I haven't done the calcs yet to see how much of an affect trajectory differences can realistically have on the relative positions of the BDC lines, but it wouldn't surprise me if it's significant. Then again, maybe it's not. I'll try to run through some calcs this weekend and maybe post the results. Jimmy |
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Yeah this is pretty hairy because even if I take an ACOG and make "adjustments" for my particular setup, the BDC could still be off. What I mean is depending on given parameters, I believe the distance between the 400 & 600 lines on the BDC hairs in the reticle could be different. I might make adjustments so the 400 line is on, but then the 600 line could be off, unlless I go with the recommended or default setup. I haven't done the calcs yet to see how much of an affect trajectory differences can realistically have on the relative positions of the BDC lines, but it wouldn't surprise me if it's significant. Then again, maybe it's not. I'll try to run through some calcs this weekend and maybe post the results. Jimmy I've found that it's either going to be pretty good or it isn't. The tacked ACOG chart is a good starting point. The real beauty is the TA11C is a near perfect match for 75/77 grain ammo out of a 16" AR when mounted to a flat top receiver. I have had excellent results with this setup at ranges out to 500+ meters. Another good example is my TA55A, it's BDC is not really suitable for anything but a 18-20" shooting 5.56 75gr ammo out to about 800 meters. But it's also a good match to M855 out to a bit over 500 meters from a 14.5" weapon. Of course you can figure your own dope for each mark with any ammo/rifle combination. But it sure helps when it's on. |
| Okay so aside from the mass of confusion having to do with matching ACOG to a particular rifle platform, what about iron sights. If I mount an ACOG do I have to remove my stock, fixed sights? I assume that if I were to mount the scope on top of the handle then the answer is no? If I mount it on the flat-top then obviously the rear iron sight will go, but what about the front sight? Can I leave it on there... I guess it would serve no purpose at this point? |
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Generally no problem with the front site, with the 4x magnification on my TA33F you can't even see the FSB. I've no experience with low magnification ACOGS, but have no trouble with the FSB and Aimpoints, so it shouldn't be an issue.
Just a suggestion, I'd recommend avoiding a carry-handle mount. Puts the scope up pretty high and makes getting a good cheek weld difficult. Of course, if you have a fixed carry handle upper you'll have no choice. Just for fun, here's some reticle pix of my TA33F 
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I have compiled several spreadsheets including numerous ballistic trajectories and ACOG BDC calibrations. Please don't ask me to post them as I was specifically requested not to do so by some of the input data providers.
If you have a particular combination in mind, then I will be more than happy to try and assist. While these data points have assisted in selecting from the numerous available configurations to get one close for a given platform, at the end of the day, it all comes down to DOPE'ing through actual live fire at various ranges. |
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I have compiled several spreadsheets including numerous ballistic trajectories and ACOG BDC calibrations. Please don't ask me to post them as I was specifically requested not to do so by some of the input data providers. If you have a particular combination in mind, then I will be more than happy to try and assist. While these data points have assisted in selecting from the numerous available configurations to get one close for a given platform, at the end of the day, it all comes down to DOPE'ing through actual live fire at various ranges. What is this, top secret information? This shouldn't take a secret clearance. I've got a Colt LE6920 (16 inch barrel). Can I count on the BDC on these things? If the behavior of ACOGs is really as unpredictable based on platform as I've been led to believe, it sounds like I'm better off just mounting the inexpensive Simmons scope from my 10/22 onto my AR and calling it a day. Plus I'll save myself $1000+. All I want to do is hit what I'm aiming at... JH |
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I have compiled several spreadsheets including numerous ballistic trajectories and ACOG BDC calibrations. Please don't ask me to post them as I was specifically requested not to do so by some of the input data providers. If you have a particular combination in mind, then I will be more than happy to try and assist. While these data points have assisted in selecting from the numerous available configurations to get one close for a given platform, at the end of the day, it all comes down to DOPE'ing through actual live fire at various ranges. What is this, top secret information? This shouldn't take a secret clearance. I've got a Colt LE6920 (16 inch barrel). Can I count on the BDC on these things? If the behavior of ACOGs is really as unpredictable based on platform as I've been led to believe, it sounds like I'm better off just mounting the inexpensive Simmons scope from my 10/22 onto my AR and calling it a day. Plus I'll save myself $1000+. All I want to do is hit what I'm aiming at... JH Nope it is not "top secret", but when a manufacturer's rep. specifically asks me not to post proprietary information which was given to me in confidence, I respect their request. As others such as Edwin have mentioned, you really need to run some ballistics calcs to figure out which model(s) of ACOG will work best for your specific intended application. As you have figured out, the ACOG BDC's are not all the same; neither are the trajectories of different ammunition through different weapons. The objective is to find two that best match each other. You can "reverse engineer" the BDC calibrations from the data in the tacked thread. The next step is to run the trajectory for your intended ammunition; ideally you would base this on chrono data from your particular weapon. Then you plot the curves to see if there is a close match. You can "force" the curves to fit better by changing your zero distance. If there is a particular distance or range of distances for which there is still an offset, then you make note of it on your DOPE table. Lastly, you actually shoot the weapon at various distances to verify your DOPE. Yes, it does take some effort. Oh, I almost forgot, here is a link to a free online ballistics calculator: JBM Ballistics Calculator |
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Nope it is not "top secret", but when a manufacturer's rep. specifically asks me not to post proprietary information which was given to me in confidence, I respect their request. As others such as Edwin have mentioned, you really need to run some ballistics calcs to figure out which model(s) of ACOG will work best for your specific intended application. As you have figured out, the ACOG BDC's are not all the same; neither are the trajectories of different ammunition through different weapons. The objective is to find two that best match each other. You can "reverse engineer" the BDC calibrations from the data in the tacked thread. The next step is to run the trajectory for your intended ammunition; ideally you would base this on chrono data from your particular weapon. Then you plot the curves to see if there is a close match. You can "force" the curves to fit better by changing your zero distance. If there is a particular distance or range of distances for which there is still an offset, then you make note of it on your DOPE table. Lastly, you actually shoot the weapon at various distances to verify your DOPE. Yes, it does take some effort. Oh, I almost forgot, here is a link to a free online ballistics calculator: JBM Ballistics Calculator Okay thanks for the advice. It's understandable that Trijicon cannot be expected to post ballistic info for every possible combo of gun, ammo, etc and I have no prob running ballistics for my particular configuration. I'm just surprised that there isn't info readily available stating for a particular ACOG what configuration it is designed for...? JH |
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