Posted: 12/31/2009 5:49:47 PM EDT
| I am looking at buying an ACOG for a16" ar platform in 7.62. I know the 7.62 ACOGs are generally calibrated for 20" barrels so would the 5.56 versions be a closer match than the those in that caliber? Thanks. |
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http://www.ar15.com/forums/topic.html?b=3&f=18&t=229420
.308 Carry-Handle BDC This BDC is based on a carry handle ACOG firing M852 Match out of a 20" barrel. ACOGs using this BDC include the TA11C and TA01B. Stats used to figure BDC baseline: M852 traveling at 2,500fps with a BC of .447 and a height over bore of 3.5" For a Flattop 20" barrel firing M852: Sight in at 150 or 0.7" high at 100. You will not deviate more than 0.5" from the BDC all the way out to 600 For a Flattop 20" firing 75gr OTM @2750fps Sight in at 100 per manual. You'll be dead on to 200, 1" high at 300, 3" high at 400, 6.7" at 500, and a bit over 10" high at 600. For a Carry Handle 20" firing 75gr OTM Sight in at 100 per manual. This doesn't match the .308 BDC too well; but it is the best you'll get. 1" high at 200, 3" high at 300, 5" high at 400, 10" at 500 and 15" high at 600. For a Flattop 16" firing 75gr OTM @2615fps Sight in at 100 per manual. This is a real close match. Max deviation is 2" at 600m and you'll be within 1" at all other ranges. For a Carry Handle 16" firing 75gr OTM Sight in at 100 per manual (for a slight edge, sight in at 125 but if you are good enough to notice the edge, then you probably want a more precise match anyway. You'll be about half MOA out to 600. There is no data for other .308 rounds or 68gr OTM because I don't have the necessary info to figure it out. If somebody gets me the 68gr info I'll add it; but those wishing SMK data or additional .308 data will need to run the numbers themselves (although I can offer help if you need it). There is no data for 55gr or 62gr because the .308 BDC is by and large a bad match for these rounds. As you can see the .308 BDC is an excellent match for the 5.56mm 75gr OTM in most applications. The TA11E uses a flattop adapter. If the BDC is designed for flattop mounting (2.5" height over bore), this ACOG will be more difficult to match to 75gr OTM use. Use the sight-in procedures given for the regular .308 BDC but figure an extra 1" high at 200, 2" high at 300, 3" high at 400 and so on. |
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