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Posted: 11/7/2006 7:45:30 PM EDT
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I just picked up an ACOG a few weeks ago. It is the TA31F which is the BAC Model with Chevron Reticle. It came with the flat top mount. I have a few questions. 1) Does the ranging reticle(BDC) only work right when it is mounted on the flat top? 2) If I use the 0.5 inch spacers to raise the unit up over the front sight will that mess with the ranging reticle(BDC)? 3) Will mounting the SCOG on a A3 Carry Handle mess with the BDC? |
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1. Yes, the TA31F was calibrated to work with a flattop 20" shooting 62 gr. M855. 2. Most likely. 3. Why would you possibly want to mount an ACOG designed for a flattop to a removable carry handle. It'll mess your BDC, POI and likely won't hold zero.. Hope this helps. |
Except that velocity is dependent on barrel length, so it is affected. In addition, changing height over bore (flat top vs. carry handle) changes BDC as well. |
Then he's not too smart, because range estimation and BDC are two separate things. First you estimate range, then you use the BDC to compensate for the drop. The BDC is calibrated for a length, and is affected by changes in that, no two ways about it. |
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I asked Trijicon the same question before and this is the response I got. I need to ask them if the TA31F is for a 16" barrel (M4 14.5"). John Houghton @ Trijicon writes: Thank you for your patronage of Trijicon products. The TA31F is calibrated for a specific height above bore which is for a flat top application. If you place this ACOG on a carry handle you will be off approximately 1 moa every 100 meters. 300 meters you will be approximately 3” off etc. If you focus your eyes on the target you typically will not notice the front sight which will appear to be a shadow in the lower portion of your sight picture. Then he wrote this: The TA31F is the best ACOG for those who are going to switch the optic between weapons with different barrel lengths/bullet weights. The TA31F was calibrated with a 62 grain bullet traveling at 3,050 fps. This calibration was done by our engineers using a commercial ballistics calculator. The 3,050 fps is basically an average velocity of .223 ammunition and a 14.5-20” barrel. The height above bore used was for flat top mounting using the supplied TA51 mount. There are too many variables to list that will affect the trajectory of a particular round/rifle combination. Typically if different bullet weight/velocities are used the farther the shot taken the more the bullet drop compensator will be affected. If you use a flat top calibrated scope on a carry handle you will see approximately a 1 moa difference every 100 meters in the calibration |
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You can mount it on a carry handle, but if you have a flat-top why elevate it? The ACOG is 4x and that will make the FSB invisible. Leave the carry handle in your LBE as a BUIS and just put the ACOG on the flat-top like it was meant to be. If you're going to remove it more than once, get the LaRue mount. |
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