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Posted: 4/26/2016 8:42:46 PM EDT
| I'm really leaning towards getting one of these for a recent purchase. I wanted to know how "off" is the BDC reticle when you use 147 grain ball? For the life of me can't figure out why Trijicon went with 168 grains with the .308 ACOGs. I could maybe see 175 since M118LR is in the supply chain but 168 hasn't been in use for a while. |
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I don't have specific numbers. I used to worry about the minutiae of slightly differing BDCs, and could have told you back then, but I learned to quit caring. If you do most of your shooting at short-mid range (0-400/500m ish?) it really doesn't matter much. You're usually off more from accuracy constraints of the low magnification, ammunition, and rifle you'll be using more than the BDC.
If you're mostly shooting at 500m+ it begins to matter more and more, or if you're shooting for bench level accuracy. But in either of those scenarios, an ACOG'd combat rifle is ill suited to that role anyway. Lastly, consider that the individual BC of the specific bullet often matters more than the specific grain. Compound this with unaccounted for changes in air pressure/humidity/shot angle/etc and it all becomes clear how geared towards 'combat accuracy' they are. At the end of the day, I've used .308 ACOGs on .223, and 20" 62gr BDCs with 12.5" SBRs firing 77gr. All with negligible changes at shooting distances I realistically shoot at. I realize none of this answers your question, but I feel that if you look into this line of thinking and practice it you'll notice you shoot 99% the same in 99% of scenarios, while worrying less, and getting more enjoyment from your shooting. |
| Thanks for your reply, the range that I shoot at goes to 1k and while I don't expect to shoot that far with the ACOG I was hoping to get out to 600. From what I read elsewhere just recently I have found out I should be 2.2 inches off at 500 so I would imagine I would be about 8 inches off at 600. This is acceptable to me for a combat optic and ball ammo. |
| It won't make much of a difference. Look up the MOA/mil drop on the reticle and just match it "close enough" with a 147 trajectory from your rifle. May end up wanting to sight in .5-1" high or whatever at 100 which would probably leave you high out to 300 and then slightly low from 400-600 vs being a lot lower at 600. |
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Quoted:
It won't make much of a difference. Look up the MOA/mil drop on the reticle and just match it "close enough" with a 147 trajectory from your rifle. May end up wanting to sight in .5-1" high or whatever at 100 which would probably leave you high out to 300 and then slightly low from 400-600 vs being a lot lower at 600. This works and really mitigates any difference. If you sight in POA/POI at 100m you'll be further and further off at distance, sometimes reaching unacceptable margins of error of using very mismatched combinations at extended range. Instead, take your max intended range, and zero (using a ballistics calculator) at about 2/3 that range. I prefer that to half-range given the exponential drop nature of bullets over distance. I usually end up around 1" high at 100m when I do this, depending on bullet/barrel/BDC, and usually I can figure it to being within MOA to the range the rifle is used for, and often a lot further. PS: To do this in practice: 1. Download a ballistics calculator 2. Input the BDC reticle information as the first load (eg M855 MV/BC, or whatever your ACOG is setup for) 3. Set ranges to increments of 100m to the range you plan on shooting 4. Input your specific setup (MV, BC, etc) as the second load 5. Play with the zero distance to what closest matches trajectory in Step 2 within the range envelope you will be shooting at 6. After selecting zero distance, zero with the prescribed offset at 100m (most of mine end up at +1-1.5") 7. ??? 8. Profit |
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The 5.56 BDCs shouldn't be too far off. Figure out your velocity and plug in the data it should be close.
Eta: meant to say on Strelok app so I ran some info using streloks BC data and a muzzle velocity for an 18" barrel listed on the factory chrono data page I think under the ammo faq and if you have a M855 reticle for carbines dial in an 1.25 inches high at 100 meters you'll be on track. Your results may vary don't take my word for it. |
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Quoted:
This works and really mitigates any difference. If you sight in POA/POI at 100m you'll be further and further off at distance, sometimes reaching unacceptable margins of error of using very mismatched combinations at extended range. Instead, take your max intended range, and zero (using a ballistics calculator) at about 2/3 that range. I prefer that to half-range given the exponential drop nature of bullets over distance. I usually end up around 1" high at 100m when I do this, depending on bullet/barrel/BDC, and usually I can figure it to being within MOA to the range the rifle is used for, and often a lot further. PS: To do this in practice: 1. Download a ballistics calculator 2. Input the BDC reticle information as the first load (eg M855 MV/BC, or whatever your ACOG is setup for) 3. Set ranges to increments of 100m to the range you plan on shooting 4. Input your specific setup (MV, BC, etc) as the second load 5. Play with the zero distance to what closest matches trajectory in Step 2 within the range envelope you will be shooting at 6. After selecting zero distance, zero with the prescribed offset at 100m (most of mine end up at +1-1.5") 7. ??? 8. Profit Quoted:
Quoted:
It won't make much of a difference. Look up the MOA/mil drop on the reticle and just match it "close enough" with a 147 trajectory from your rifle. May end up wanting to sight in .5-1" high or whatever at 100 which would probably leave you high out to 300 and then slightly low from 400-600 vs being a lot lower at 600. This works and really mitigates any difference. If you sight in POA/POI at 100m you'll be further and further off at distance, sometimes reaching unacceptable margins of error of using very mismatched combinations at extended range. Instead, take your max intended range, and zero (using a ballistics calculator) at about 2/3 that range. I prefer that to half-range given the exponential drop nature of bullets over distance. I usually end up around 1" high at 100m when I do this, depending on bullet/barrel/BDC, and usually I can figure it to being within MOA to the range the rifle is used for, and often a lot further. PS: To do this in practice: 1. Download a ballistics calculator 2. Input the BDC reticle information as the first load (eg M855 MV/BC, or whatever your ACOG is setup for) 3. Set ranges to increments of 100m to the range you plan on shooting 4. Input your specific setup (MV, BC, etc) as the second load 5. Play with the zero distance to what closest matches trajectory in Step 2 within the range envelope you will be shooting at 6. After selecting zero distance, zero with the prescribed offset at 100m (most of mine end up at +1-1.5") 7. ??? 8. Profit This is the right advice. The key is knowing what your muzzle velocity is. |
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