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Posted: 4/9/2009 12:01:44 PM EDT
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Ok guys im a newbie on this Board and just bought my first personal Firearm in the form of a DPMS LR 308 A4 (16in Barrel 1/10 twist). Im active duty military and SDM trained so the AR family is pretty much instinct for me by now. I want to put an AGOG on it and my question is since an ACOG's bullet drop comp is for Mil Spec Ammo(i think) how much would match grade ammo then be thrown off because of the difference in ballistics. Or Have i answered my own question?
Chris |
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I'm guessing you are comparing 147 grain 308 Ball to 168 grain OTM. Out to 400 yards, less difference than the width of the BDC crosshatches in the 308-based ACOG. Beyond 400 yds/meters you'll likely start to see a difference.
FYI, I doubt a 308-calibrated ACOG is setup for 16" velocities. Probably setup for 20+" barrels of an SR-25 or M14. You might call Trijicon. They're responsive, in my experience. Also, you might look into the new ACOG-like optic Burris is releasing any time now. About 1/5 the cost. Not as rugged, but ALOT cheaper. -David Edgewood, NM |
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BDC are not at all precise. But they do give a close guess. There are so many variables the further out you go, the harder it is to stay on target.
So far as I can tell the starting point is: Trijicon BDC baseline: M852, 168gr, traveling at 2,500fps with a BC of .447 and a height over bore of 3.5" so really what you need to do is run some ballistics numbers with those above and yours for your particular rifle and load, and compare. Using those numbers and a basic ballistic calculator: Range Velocity Impact Drop ToF Energy Drift 0 2500 -3.5 0 0 2332 0 50 2400 -0.99 0.84 0.06 2149 0.64 100 2307 0 3.19 0.13 1985 1.28 150 2216 -0.65 7.19 0.19 1832 2.36 200 2126 -3.07 12.96 0.26 1686 3.91 250 2039 -7.43 20.66 0.34 1551 5.96 300 1954 -13.88 30.46 0.41 1424 8.54 350 1871 -22.61 42.54 0.49 1306 11.67 400 1791 -33.84 57.11 0.57 1197 15.41 450 1713 -47.78 74.4 0.66 1095 19.77 500 1638 -64.68 94.65 0.75 1001 24.79 550 1566 -84.83 118.14 0.84 915 30.52 600 1497 -108.51 145.17 0.94 836 36.97 650 1432 -136.06 176.07 1.04 765 44.19 700 1370 -167.84 211.19 1.15 700 52.21 750 1313 -204.23 250.93 1.26 643 61.03 800 1260 -245.65 295.69 1.38 592 70.67 So the above should be the base line–– BUT Trijicon is in meters, and those are in yards. So... thats more math than I want to do right now. So use a ballistic calculator like this one punch in your numbers and see. My experience is that since 2500 is a little slow for most of my loads, I am a little high at the beginning. But since they have a better BC than cheaper bullets, over time my rounds drop more. So out to 400 or so I am good. Ref numbers found here |
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