AR Sponsor
Posted: 3/21/2016 2:16:38 AM EDT
|
Hi,
I have a question I was hoping y'all could help me with. Is there a way I could zero my 11.5" SBR running MK262 @ 2450fps and have my ACOG (TA31 ECOS, TA31F) or my ELCAN so that the BDC would be back on? (I.E. Zero 2" high at 100 and you'll be back on) Thanks |
|
I'm going to show my work since ballistics calculation is new for me.
TA31F is calibrated for 62gr @ 3050 fps. MK262 ballistic coefficient is .373 vs. .304 for M855 (which is what I assume Trijicon used as their 62 gr load). So using this data, the subtensions should work out to... 100m - 0 moa 200m - 1.5 moa 300m - 4.3 moa 400m - 7.9 moa 500m - 12.5 moa 600m - 18.4 moa 700m - 25.9 moa 800m - 35.1 moa MK262 zeroed at 100 meters works out to: 100m - 0 moa 200m - 2.8 moa 300m - 7 moa 400m - 12.2 moa 500m - 18.7 moa 600m - 26.5 moa 700m - 35.9 moa 800m - 46.8 moa Putting those side by side M855 MK262 100m - 0 moa 0 moa 200m - 1.5 moa 2.8 moa 300m - 4.3 moa 7 moa 400m - 7.9 moa 12.2 moa 500m - 12.5 moa 18.7 moa 600m - 18.4 moa 26.5 moa 700m - 25.9 moa 35.9 moa 800m - 35.1 moa 46.8 moa You can see that at 300m, the MK 262 should be pretty damn close to zeroed at 400m on the TA31F and that remains true through to 700m (ie just use one 100m higher at 300m and beyond) At 200m, the 200m mark will hit 1.3moa low (2.5 inches), which is pretty close for this type of optic. So long story short, using the TA31F with MK262 @ 2450fps, with 100m zero, you should be hitting about 2.5 inches low at the 200m reticle mark (1.3moa), and be very close to zeroed (certainly close enough for a combat optic at that range) at 300m at the 400m mark, 400m at the 500m mark, and so forth out to the 800m mark. Like I said, this is all pretty new to me so if I screwed anything up, someone help me out! |
|
I never figured out BDC based on MOA. I do it by inches.
2,450 velocity and a 100 yard zero w 2.5" sight height: -300 yards 62g drops 35.64" and hits 19.73" low. -300 yards 77g 262 drops 32.91" and hits 17.84" low. At 400 yards 62g impacts 5" lower. At 500 yards 62g impacts 11" lower. At 600 yards 62g impacts 20" lower. This is with .373 and .304 BC I would think that the margin of error from the user on identifying and holding the scope on target would make a bigger difference than the actual drop difference of the optic. 2,450, 62g, .304, 2.5: sight height RangeVelocityImpactDropToFEnergyDrift 02450-2.5008260 202388-1.490.170.037850 402333-0.720.580.057490 602279-0.211.250.087150 8022250.032.190.116820 100217203.40.136490 1202119-0.334.920.166180 1402067-0.976.740.195880 1602016-1.958.90.225600 1801966-3.2611.390.255320 2001917-4.9414.250.285060 2201868-6.9917.480.314800 2401820-9.4521.120.344560 2601774-12.3225.170.384330 2801728-15.6429.670.414110 3001683-19.4334.640.453900 3201639-23.6940.090.483700 3401596-28.4946.070.523510 3601554-33.8352.590.563320 3801513-39.7559.690.63150 4001473-46.2867.40.642990 4201435-53.4475.740.682840 4401397-61.2984.770.722690 4601362-69.8494.50.762550 4801327-79.15104.990.812420 5001295-89.24116.260.862310 5201263-100.15128.360.92200 5401234-111.94141.330.952100 5601205-124.64155.2112000 5801179-138.3170.051.051910 6001154-152.95185.881.11830 2,450, 77g, .373, 2.5" sight height RangeVelocityImpactDropToFEnergyDrift 02450-2.50010260 202400-1.50.170.039850 402355-0.740.580.059480 602310-0.231.240.089120 8022660.022.160.18780 100222203.360.138440 1202179-0.34.830.168120 1402136-0.96.60.197800 1602094-1.818.680.217500 1802052-3.0311.070.247200 2002011-4.5913.80.276910 2201970-6.4916.870.36640 2401929-8.7520.30.336360 2601890-11.3924.110.376110 2801851-14.428.30.45860 3001812-17.8432.910.435610 3201774-21.6937.930.465380 3401737-25.9943.40.55160 3601700-30.7549.330.534940 3801664-3655.750.574730 4001628-41.7462.660.614530 4201593-48.0170.10.644340 4401559-54.8378.090.684160 4601526-62.2186.650.723980 4801493-70.295.810.763810 5001461-78.81105.590.83650 5201430-88.07116.020.843500 5401400-98.02127.140.883350 5601371-108.66138.950.933210 5801343-120.05151.510.973080 6001315-132.21164.841.022960 To decode bc I am not taking the time to split this out... 500 yard 77g line (5 from bottom). 500 yards-1461 velocity--78.81" impact-105.59" drop-0.8 TOF-365 energy-0 wind |
| This all looks like enormous over complication. Will you realistically be using your 11.5 on 400m+ targets ever? If not, why would you throw your BDC off trying to account for an increasingly off trajectory? I'd zero at half the intended range. It'll likely look roughly like +1"@100m, =@200m, and -3"@300m, ish. All within MOA, and all within the accuracy constraints of the rifle. This doesn't address your question, but if you look into this I feel you will likely find it is the best strategy for your needs. |
|
I really appreciate all the replies!
I was running some numbers through ballisticAE and so far I'm coming up with 2" high at 100yds will put my BDC on out to 400, within 2" or so. The numbers I'm running are: M855 @ 2950 77gr SMK @ 2450 And yes, I do toutenly shoot my sbr out to 400+ all the time. It's my primary go to rifle. The gun is easily running 1moa or better five shot groups with the mk262 ammo so it is beyond capable accuracy wise to make the 400+yd shots. I just need to get my BDC lined up a little better so it's a little easier to make those hits. |
| Without checking, your numbers look pretty close to a similar setup. My 12.5 with a 31f reticle is about 1-1.5" high at 100m with 77tmk. This gave me the best compromise out to 300m. If you wanted to get any closer to BDC I'd almost think you'd need a 6.8 or 7.62 reticle, though I'd think the juice wouldn't be worth the squeeze unless you're very OCD about it and really trying to target shoot with a 4X optic. |
|
Quoted:
I really appreciate all the replies! I was running some numbers through ballisticAE and so far I'm coming up with 2" high at 100yds will put my BDC on out to 400, within 2" or so. The numbers I'm running are: M855 @ 2950 77gr SMK @ 2450 And yes, I do toutenly shoot my sbr out to 400+ all the time. It's my primary go to rifle. The gun is easily running 1moa or better five shot groups with the mk262 ammo so it is beyond capable accuracy wise to make the 400+yd shots. I just need to get my BDC lined up a little better so it's a little easier to make those hits. According to what I ran on strelok, if you zero at 100 yards and go 2 MOA up you're pretty much on if you read the reticle in yards instead of meters. The 800 stadia will be 823 (probably close enough). |
|
Quoted:
According to what I ran on strelok, if you zero at 100 yards and go 2 MOA up you're pretty much on if you read the reticle in yards instead of meters. The 800 stadia will be 823 (probably close enough). Quoted:
Quoted:
I really appreciate all the replies! I was running some numbers through ballisticAE and so far I'm coming up with 2" high at 100yds will put my BDC on out to 400, within 2" or so. The numbers I'm running are: M855 @ 2950 77gr SMK @ 2450 And yes, I do toutenly shoot my sbr out to 400+ all the time. It's my primary go to rifle. The gun is easily running 1moa or better five shot groups with the mk262 ammo so it is beyond capable accuracy wise to make the 400+yd shots. I just need to get my BDC lined up a little better so it's a little easier to make those hits. According to what I ran on strelok, if you zero at 100 yards and go 2 MOA up you're pretty much on if you read the reticle in yards instead of meters. The 800 stadia will be 823 (probably close enough). That's kinda what I was coming up with too. I do read the reticle in yards, mostly because I don't do a damn thing in the metric system lol. |
|
Quoted:
I'm going to show my work since ballistics calculation is new for me. TA31F is calibrated for 62gr @ 3050 fps. MK262 ballistic coefficient is .373 vs. .304 for M855 (which is what I assume Trijicon used as their 62 gr load). So using this data, the subtensions should work out to... 100m - 0 moa 200m - 1.5 moa 300m - 4.3 moa 400m - 7.9 moa 500m - 12.5 moa 600m - 18.4 moa 700m - 25.9 moa 800m - 35.1 moa MK262 zeroed at 100 meters works out to: 100m - 0 moa 200m - 2.8 moa 300m - 7 moa 400m - 12.2 moa 500m - 18.7 moa 600m - 26.5 moa 700m - 35.9 moa 800m - 46.8 moa Putting those side by side M855 MK262 100m - 0 moa 0 moa 200m - 1.5 moa 2.8 moa 300m - 4.3 moa 7 moa 400m - 7.9 moa 12.2 moa 500m - 12.5 moa 18.7 moa 600m - 18.4 moa 26.5 moa 700m - 25.9 moa 35.9 moa 800m - 35.1 moa 46.8 moa You can see that at 300m, the MK 262 should be pretty damn close to zeroed at 400m on the TA31F and that remains true through to 700m (ie just use one 100m higher at 300m and beyond) At 200m, the 200m mark will hit 1.3moa low (2.5 inches), which is pretty close for this type of optic. So long story short, using the TA31F with MK262 @ 2450fps, with 100m zero, you should be hitting about 2.5 inches low at the 200m reticle mark (1.3moa), and be very close to zeroed (certainly close enough for a combat optic at that range) at 300m at the 400m mark, 400m at the 500m mark, and so forth out to the 800m mark. Like I said, this is all pretty new to me so if I screwed anything up, someone help me out! Pretty sure you're confusing MOA with inches. At 400 meters there's a 4.3 MOA difference, so that's equal to approximately 17.2 inches. At 500 meters there's a 6.2 MOA difference, so that's a 31 inch difference. At 800 meters you're going to be off by approximately 85.6 inches. MOA is a measure of an angle, not a discrete measurement of length. That length is a function of the amount of angle at distance. |
|
Quoted:
Pretty sure you're confusing MOA with inches. At 400 meters there's a 4.3 MOA difference, so that's equal to approximately 17.2 inches. At 500 meters there's a 6.2 MOA difference, so that's a 31 inch difference. At 800 meters you're going to be off by approximately 85.6 inches. MOA is a measure of an angle, not a discrete measurement of length. That length is a function of the amount of angle at distance. Quoted:
Quoted:
I'm going to show my work since ballistics calculation is new for me. TA31F is calibrated for 62gr @ 3050 fps. MK262 ballistic coefficient is .373 vs. .304 for M855 (which is what I assume Trijicon used as their 62 gr load). So using this data, the subtensions should work out to... 100m - 0 moa 200m - 1.5 moa 300m - 4.3 moa 400m - 7.9 moa 500m - 12.5 moa 600m - 18.4 moa 700m - 25.9 moa 800m - 35.1 moa MK262 zeroed at 100 meters works out to: 100m - 0 moa 200m - 2.8 moa 300m - 7 moa 400m - 12.2 moa 500m - 18.7 moa 600m - 26.5 moa 700m - 35.9 moa 800m - 46.8 moa Putting those side by side M855 MK262 100m - 0 moa 0 moa 200m - 1.5 moa 2.8 moa 300m - 4.3 moa 7 moa 400m - 7.9 moa 12.2 moa 500m - 12.5 moa 18.7 moa 600m - 18.4 moa 26.5 moa 700m - 25.9 moa 35.9 moa 800m - 35.1 moa 46.8 moa You can see that at 300m, the MK 262 should be pretty damn close to zeroed at 400m on the TA31F and that remains true through to 700m (ie just use one 100m higher at 300m and beyond) At 200m, the 200m mark will hit 1.3moa low (2.5 inches), which is pretty close for this type of optic. So long story short, using the TA31F with MK262 @ 2450fps, with 100m zero, you should be hitting about 2.5 inches low at the 200m reticle mark (1.3moa), and be very close to zeroed (certainly close enough for a combat optic at that range) at 300m at the 400m mark, 400m at the 500m mark, and so forth out to the 800m mark. Like I said, this is all pretty new to me so if I screwed anything up, someone help me out! Pretty sure you're confusing MOA with inches. At 400 meters there's a 4.3 MOA difference, so that's equal to approximately 17.2 inches. At 500 meters there's a 6.2 MOA difference, so that's a 31 inch difference. At 800 meters you're going to be off by approximately 85.6 inches. MOA is a measure of an angle, not a discrete measurement of length. That length is a function of the amount of angle at distance. No I get that, I'm saying if you use the 400m marker for 300m, the 500m marker for 400m, etc., that the difference between the POA and POI is within 1 MOA, which for the purposes of an 11.5" SBR is plenty damn close. So for a 300m your POI would be within 3 inches if you used the 400m reticle as POA, and at 700m your POI would be within 7 inches if you used the 800m reticle as POA. Unless I'm still missing something or used Hornady's ballistics calculator incorrectly. |
|
Quoted:
This all looks like enormous over complication. Will you realistically be using your 11.5 on 400m+ targets ever? If not, why would you throw your BDC off trying to account for an increasingly off trajectory? I'd zero at half the intended range. It'll likely look roughly like +1"@100m, =@200m, and -3"@300m, ish. All within MOA, and all within the accuracy constraints of the rifle. This doesn't address your question, but if you look into this I feel you will likely find it is the best strategy for your needs. This |
|
Quoted:
I really appreciate all the replies! I was running some numbers through ballisticAE and so far I'm coming up with 2" high at 100yds will put my BDC on out to 400, within 2" or so. The numbers I'm running are: M855 @ 2950 77gr SMK @ 2450 And yes, I do toutenly shoot my sbr out to 400+ all the time. It's my primary go to rifle. The gun is easily running 1moa or better five shot groups with the mk262 ammo so it is beyond capable accuracy wise to make the 400+yd shots. I just need to get my BDC lined up a little better so it's a little easier to make those hits. If you're shooting out 400+ all the time, just hold where you hold when you get hits at 400? The bdc will not line up by just zeroing 2" high or something. Trajextory will get further and further off the BDC the further away you ho. |
|
Quoted:
If you're shooting out 400+ all the time, just hold where you hold when you get hits at 400? The bdc will not line up by just zeroing 2" high or something. Trajextory will get further and further off the BDC the further away you ho. Quoted:
Quoted:
I really appreciate all the replies! I was running some numbers through ballisticAE and so far I'm coming up with 2" high at 100yds will put my BDC on out to 400, within 2" or so. The numbers I'm running are: M855 @ 2950 77gr SMK @ 2450 And yes, I do toutenly shoot my sbr out to 400+ all the time. It's my primary go to rifle. The gun is easily running 1moa or better five shot groups with the mk262 ammo so it is beyond capable accuracy wise to make the 400+yd shots. I just need to get my BDC lined up a little better so it's a little easier to make those hits. If you're shooting out 400+ all the time, just hold where you hold when you get hits at 400? The bdc will not line up by just zeroing 2" high or something. Trajextory will get further and further off the BDC the further away you ho. It doesn't work like that. Look at the second picture I posted. He is off at most an inch and a half at 100y, dead on at 300y and then off a little bit further. If he has a POI = POA at 100y the .6 or 1.3 MOA offset gets added to every other distance. If he was close at 600m on the right picture, it would put him 10" further off. If being off 1.5" at 100y matters to you, why are you using an ACOG with BDC? |
AR Sponsor