180 AB bc

[RockyMtnMT]

Hey guys,

Anybody got a real world bc on the .308 cal 180 AB running around 3400fps. Shot some this weekend and can't get the drops to match published bc. Just want to know if I have some other data wrong or if it is the bc.

Thanks

Steve

 

[Ridgerunner665]

Litz tested the 180 AB and came up with .493.... page 10 in the link.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA554683


I tested the 168 BT and came up with .475 (advertised at .490)...I tested the old fashioned way though, LOL...shot them and made the numbers match.

 

[RockyMtnMT]

Having to run .43 bc to match the drop at 980 yrds. It really makes no sense. Everything else has to be so far off from the collected data to get the drop to work. Velocity and zero yardage are the two big ones. Everything else makes only very small changes. Where could I have gone wrong?

Steve

 

[Ridgerunner665]

Are you taking into account all the atmospheric data? What are you using to generate the drop data? A lot of little things add up to big things...


Scope height or muzzle velocity would be the first things I double checked...chrono's can be contrary gadgets at times.'


Could even be the load itself...if you used a powder that is prone to changes with temperature...

 

[RockyMtnMT]

Are you taking into account all the atmospheric data? What are you using to generate the drop data? A lot of little things add up to big things...


Scope height or muzzle velocity would be the first things I double checked...chrono's can be contrary gadgets at times.'


Could even be the load itself...if you used a powder that is prone to changes with temperature...

Ballistic ftp on ipod, jbm, and another. All come in the same. Chrono reading is basically the same as another rifle with the same load. Scope height changes make very little change in the drop on the programs.

The only thing that I can make sense of is a the zero range being wrong. To match the drops I would have to be off by 5" at 300 yrds. That just wasn't the case. Chrony reading was at 3340fps, would have to be wrong by nearly 200fps to match the drop. That could be it. But other rifles shot on the same day ran ballistics fine with the same chrony.

Not a big deal. Just frustrating.

Steve

 

[Ridgerunner665]

Yeah...I'm just tossing out ideas that I thought may help narrow it down.

 

[BryanLitz]

Have you verified that your scope is tracking true?

In other words, when you dial 30 MOA of elevation (for example), does your scope actually move your point of aim 30 MOA? It's common for scopes to not track true. Test at short range to verify.

Good luck,
-Bryan

 

[RockyMtnMT]

That makes the most sense. A guy always looks past the scope and assumes that it is doing what it should. Especially when you have others of the same model working fine.

Steve