Help truing BC

[powereng]

I use Shooter as my ballistic solver. I’ve struggled for years now try to get shooter to align with my real world hits. The thread on truing your software by adjusting your BC instead of adjusting your velocity led me to do some testing today.

Here is how I have Shooter set up:

Sierra 175.0gr MatchKing (Litz)
Bullet Diameter: 0.308 in
Bullet Weight: 175.0 gr
Bullet Length: 1.24 in
Muzzle Velocity: 2650 fps (MegnetoSpeed)
Atmosphere Std: ICAO
Drag Model: G7
BC 0.243 Min Velocity 0 FPS
Zero Range: 100 yds

Station Pressure: 29:94 inHg
Pressure absolute
Temp: 50^F
Humidity: 71.80

Rifle AE MK III
Barrel twist: 1 in 12
Sight Height: 2.2”
Scope: Kahles 624i Mils

Test
Range = 650yds
Shooter = 5.2mils, Actual = 5.2mils

Range = 872yds
Shooter = 8.8mils, Actual = 9.2mils

Range = 1004yds
Shooter = 11.5mils, Actual = 11.4/11.5

For reference, the white in the distance is a wagon where 15"x 15" practice target is set up at 872 yards. However for some reason Shooter just does not agree with this range. What other BC’s can I add to shooter to help true the software to my real world hits?

 

[Deleted member 113831]

One problem is your twist. That bullet is falling apart stability wise, by the time it gets to 872 yards. Being at sea level isn't helping it any.

 

[Sheldon N]

Test
Range = 650yds
Shooter = 5.2mils, Actual = 5.2mils

Range = 872yds
Shooter = 8.8mils, Actual = 9.2mils

Range = 1004yds
Shooter = 11.5mils, Actual = 11.4/11.5

Something's not right with your data here. No way the bullet is taking a 0.4 mil trajectory detour then coming back in line. Either your target range is wrong, or mirage, or where you thought you were impacting vs where you were actually impacting, or scope tracking or something else. Bullets should fly in a predicable fashion, and truing the BC should bring all yardages into line (assuming accurate velocity).

 

[powereng]

Sheldon, I'm not going to disagree with you. I wish I could figure it out. The coming back in line at 1004 shocked me as well. I've checked tracking at 100yds and the scope is dead on. Ranges all shot with Vectronix Terrapin. I'm going to try some more ranges tomorrow.

 

[Deleted member 113831]

Try shooting it again when it is overcast, or early as you can in the morning. If there is an optical effect messing with you, then it should be absent or at least minimized.