ACOG BDC

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From: http://www.ar15.com/archive/topic.ht...&f=18&t=302205

Not sure if those are the assumptions used for the data I posted above. Since I sold the ACOG, I ended up putting away a lot of the data I had for it. I would have to spend time digging it out.

But, I tested those # above against JBM ballistics (3050 fps, 62gr, .304 BC, 2.6" sight height), and it was dead on to 500 meters, then less than one MOA different up to 800. (600 -16.2, 700 -22.5, 800 -30.1), so it checks out pretty close.

[PrimaryArms]

From: http://www.ar15.com/archive/topic.ht...&f=18&t=302205



Not sure if those are the assumptions used for the data I posted above. Since I sold the ACOG, I ended up putting away a lot of the data I had for it. I would have to spend time digging it out.

But, I tested those # above against JBM ballistics (3050 fps, 62gr, .304 BC, 2.6" sight height), and it was dead on to 500 meters, then less than one MOA different up to 800. (600 -16.2, 700 -22.5, 800 -30.1), so it checks out pretty close.

Thats way off!
Wow!

-Dimitri

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Way off the actual ACOG subtensions or way off what it should be based on M855 out of a 20" barrel?

[PrimaryArms]

ACOG BDC

Way off the actual ACOG subtensions or way off what it should be based on M855 out of a 20" barrel?

Using the fps they provided him and data mentioned its way off!



-Dimitri

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Also, found an old thread on this:

http://www.calguns.net/calgunforum/archive/index.php/t-562798.html

[PrimaryArms]

ACOG BDC

Also, found an old thread on this:

http://www.calguns.net/calgunforum/a.../t-562798.html

I cant give out data but one of the listings looks right the rest look way off!

-Dimitri

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Nevermind, I found the problem. The military spec has the chronograph at 78 FEET from the muzzle (25 meters). Makes a huge difference. Those numbers I was using were way off. Makes me glad I never got that ACOG past 300 yards. Would have been scratching my head, since I was using tables for a custom load.

[PrimaryArms]

Nevermind, I found the problem. The military spec has the chronograph at 78 FEET from the muzzle (25 meters). Makes a huge difference. Those numbers I was using were way off. Makes me glad I never got that ACOG past 300 yards. Would have been scratching my head, since I was using tables for a custom load.

I don't think so! That would make it even more off.
The round is going high as is if the fps was at 25m add another 80fps.

-Dimitri

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More research stirs the pot further. According to one source, TA31F is a hybrid (roughly equivalent to 16"), the RCOa4 uses 20" barrel data, and the RCOm4 uses 14.5" barrel data. So, this is clear as mud. I can only guess that Dmitri's data is for the 31F, and the data Trijicon has been telling everyone is from the RCOa4? or Trijicon has been giving everyone the 31F data, and Dmitri, you're working off the 14.5" barrel data (RCOm4?) that the OP asked about?

I'm done with this. Makes me thankful once again for the ACSS HUD with published subtensions.

[acourvil]

ACOG subtentions are out there if you look hard enough for them.

If you email Trijicon and tell them the model you have, they will tell you the subtensions.

[PrimaryArms]

ACOG BDC

More research stirs the pot further. According to one source, TA31F is a hybrid (roughly equivalent to 16"), the RCOa4 uses 20" barrel data, and the RCOm4 uses 14.5" barrel data. So, this is clear as mud. I can only guess that Dmitri's data is for the 31F, and the data Trijicon has been telling everyone is from the RCOa4? or Trijicon has been giving everyone the 31F data, and Dmitri, you're working off the 14.5" barrel data (RCOm4?) that the OP asked about?

I'm done with this. Makes me thankful once again for the ACSS HUD with published subtensions.

The barrel length a side I am going off BC fps and BDC given by members. They don't match up..


-Dimitri

[ocabj]

I sort of discussed my 'verification' of the BDC on an 18" 1-7" twist SPR barrel with the TA31RCO-M150 in a write up from earlier this year.

http://www.ocabj.net/18-spr-field-rifle-build-report/

At each the 300, 500, and 600 yard lines, I found that I would use the 300, 500, and 600 meter reticles, respectively, but hold under the point of impact about halfway between center and 6 o’clock hold on the F-Class target. For those that are not familiar with official NRA High Power targets, the target black for F-Class 300 yard is 17.85″, while the target black for 500 and 600 yards F-Class are 30″ and 36″, respectively.

So I was holding (aiming) about 5″ low of center on the 300 yard target using the 300 meter reticle, about 8″ low of center on the 500 yard target, using the 500 meter reticle, and about 9″ low of center on the 600″ yard target using the 600 meter reticle. If you calculate the numbers, that’s about 1.5 to 1.6 MOA low of center for all three distances.

Anyway, my opinion is that BDC's are not perfect and there's too many factors that come into play with regards to how well the BDC actually matches up your real life trajectory: e.g. ammo used, individual barrel, elevation from sea level.

If you're going to use the ACOG BDC, you should basically zero the 100 or the 200 reticle point at actual distance, and then confirm what kind of offsets you're going to see for the 300, 400, 500, 600 ... hash/reticle marks by shooting known distance.

[PrimaryArms]

ACOG BDC

I sort of discussed my 'verification' of the BDC on an 18" 1-7" twist SPR barrel with the TA31RCO-M150 in a write up from earlier this year.

http://www.ocabj.net/18-spr-field-rifle-build-report/

Anyway, my opinion is that BDC's are not perfect and there's too many factors that come into play with regards to how well the BDC actually matches up your real life trajectory: e.g. ammo used, individual barrel, elevation from sea level.

If you're going to use the ACOG BDC, you should basically zero the 100 or the 200 reticle point at actual distance, and then confirm what kind of offsets you're going to see for the 300, 400, 500, 600 ... hash/reticle marks by shooting known distance.

BDC reticles can be right on when done right. LOS is the major variant that would cause such a change in POI. Temp altitude and so on doesn't effect BDC that much. Besides 5.56 is about a 1.5-2MOA round to start off with.

-Dimitri

[Loner]

Here you go:

http://www.ar15.com/forums/t_3_18/229420_Bartholomew_Roberts__Big_ACOG_BDC_Chart.html

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This would all be so much easier if Trijicon would just publish the damn MOA drops of the subtensions.