ColoYooper
Well-Known Member
- Joined
- Feb 17, 2013
- Messages
- 53
My typical method of using current ballistics programs for a new load is to:
1) Lookup the published BC for that bullet
2) Go to the range and zero my scope at 100yrds and record Muzzle Velocity.
3) Use some ballistics calculator and determine 500 yard MOA setting.
4) Shoot at 500 yards and note actual MOA setting (which is different)
5) Use some ballistics calculator and determine 1000 yard MOA setting.
6) Shoot at 1000 yards and note actual MOA setting (which is different)
7) Play with Ballistic calculator and find BC that comes closest to observed 500 and 1000 yard actual for my muzzle velocity.
8) Use ballistics calculator to determine 1200 yard MOA setting using newly determined BC. Guess what. THE BULLET GROUPS LOW.
So what have we figured out. The published BC is a good place to start, but will need refining. And in most cases, the BC will decay as velocity decreases (as is pointed out in the Sierra Manual) So no one G1 or G7 BC curve is going to produce great results at 300, 600, 900 and 1200 yards.
So wrote my own Ballistics Calculator which is attached. This utilizes the steps I normally take anyway. You zero the rifle at 100 yards and enter the Muzzle Velocity: V0. You enter a Mid-Range distance in yards, and the MOA adjustment needed to center your group at the Mid-Range. Ideally the Mid-Range will be in the middle range of your rifles expected use. I like 500 to 600 yards. Then you enter a Long-Range distance in yards, and the MOA adjustment needed to center your group at that range. Again I like 1000 yards, but it should be toward the longer end of the use spectrum. That's it. Then just hit the GO FIGURE button. The program will output 3 important numbers: 1) the V0 muzzle velocity you entered, 2) The Vx Velocity. This would be the 100 yard velocity on the G1 or G7 curve with no BC decay. 3) The VS_SF. This is the amount the application decays the BC for each iteration. This number will be something between 99 which is no decay...to 50 which is a lot of decay. NOTE: Internally the VS_SF numbers are preceded by (5) 9s, so VS_SF of 63 is internally 0.9999963. The program then outputs expected MOA settings for various ranges on the right. You can then enter your current range and hit GO FIGURE and see the computed MOA. You can also enter the wind speed in MPH and a wind direction in clock cordinates (1..12) and see the holdoff in MILS for wind. Anyway this is early in development and I haven't written the Smart Phone App for it yet. Also in development is a Virtual Spotter, which includes this App, but also steams HD Video with a 3 second delay, from a 50x Camera to a tablet. This allows you to take the shot, and then look over at the display and see the hit or miss, with an image of your scopes crosshairs superimposed on the streaming image, and the needed holdoff required to hit the target.
Note: I spent 25 years developing Inertial Navigation systems for the Air Force and currently design Micro Processors.
1) Lookup the published BC for that bullet
2) Go to the range and zero my scope at 100yrds and record Muzzle Velocity.
3) Use some ballistics calculator and determine 500 yard MOA setting.
4) Shoot at 500 yards and note actual MOA setting (which is different)
5) Use some ballistics calculator and determine 1000 yard MOA setting.
6) Shoot at 1000 yards and note actual MOA setting (which is different)
7) Play with Ballistic calculator and find BC that comes closest to observed 500 and 1000 yard actual for my muzzle velocity.
8) Use ballistics calculator to determine 1200 yard MOA setting using newly determined BC. Guess what. THE BULLET GROUPS LOW.
So what have we figured out. The published BC is a good place to start, but will need refining. And in most cases, the BC will decay as velocity decreases (as is pointed out in the Sierra Manual) So no one G1 or G7 BC curve is going to produce great results at 300, 600, 900 and 1200 yards.
So wrote my own Ballistics Calculator which is attached. This utilizes the steps I normally take anyway. You zero the rifle at 100 yards and enter the Muzzle Velocity: V0. You enter a Mid-Range distance in yards, and the MOA adjustment needed to center your group at the Mid-Range. Ideally the Mid-Range will be in the middle range of your rifles expected use. I like 500 to 600 yards. Then you enter a Long-Range distance in yards, and the MOA adjustment needed to center your group at that range. Again I like 1000 yards, but it should be toward the longer end of the use spectrum. That's it. Then just hit the GO FIGURE button. The program will output 3 important numbers: 1) the V0 muzzle velocity you entered, 2) The Vx Velocity. This would be the 100 yard velocity on the G1 or G7 curve with no BC decay. 3) The VS_SF. This is the amount the application decays the BC for each iteration. This number will be something between 99 which is no decay...to 50 which is a lot of decay. NOTE: Internally the VS_SF numbers are preceded by (5) 9s, so VS_SF of 63 is internally 0.9999963. The program then outputs expected MOA settings for various ranges on the right. You can then enter your current range and hit GO FIGURE and see the computed MOA. You can also enter the wind speed in MPH and a wind direction in clock cordinates (1..12) and see the holdoff in MILS for wind. Anyway this is early in development and I haven't written the Smart Phone App for it yet. Also in development is a Virtual Spotter, which includes this App, but also steams HD Video with a 3 second delay, from a 50x Camera to a tablet. This allows you to take the shot, and then look over at the display and see the hit or miss, with an image of your scopes crosshairs superimposed on the streaming image, and the needed holdoff required to hit the target.
Note: I spent 25 years developing Inertial Navigation systems for the Air Force and currently design Micro Processors.
