rooshooter
New member
I,m just checking elevation needed for an up coming 1200 yd shoot and was wondering whether the default G1 setting is best to use. I had read somewhere about using G7 with modern long range bullets. 175gn 7mm sierra in my case.
G1 or G7 when using balistics programs , long range bullets
- Thread starter rooshooter
- Start date
L
Louis Boyd
Guest
While the G7 model is a better model of the drag vs velocity of a low drag boattail bullet than the G1 model no bullet manufactureer I'm aware of publishes G7 coefficients. G1 is the industy standard. Sierra bullets helps (or perhaps confuses) the situation by providing multiple G1 coefficeints for various velocity ranges.
However, if you use measured drop (or velocity or time of flight) vs range values and adjust the G7 coefficient to get a good fit, the G7 model should give a better trajectory predictions over a wide range of velocities than the G1 model for boatttail bullets It's still not likely to be a perfect match.
For a good description of the various "G" models I recommend the book "Modern Exterior Ballistics" by Robert McCoy (Ballistics Research Lab Aberdeen Proving Grounds). The military abaandoned the use of ballistic coefficients in favor of measured drag data about 40 years ago. That's why you rarely see BC values published by the military. The whole concept of using ballistic coefficients is archaic. All they accomplish is to guarantee never having accurate trajectory calculations. With the invention of computers and millimeter wave doppler radar there's little excuse for not to having complete drag functions for every model of bullet manufactured. The use of G1 coefficients is mostly to help marketing. G1 coefficients are always much larger numbers and therefore more impressive than G7 coefficients, and drag tables are of little use except as computer files.
Who would buy a 30 caliber VLD bullet with a G7 BC .47 when they can have one with a G1 BC of .67? Sigh...
However, if you use measured drop (or velocity or time of flight) vs range values and adjust the G7 coefficient to get a good fit, the G7 model should give a better trajectory predictions over a wide range of velocities than the G1 model for boatttail bullets It's still not likely to be a perfect match.
For a good description of the various "G" models I recommend the book "Modern Exterior Ballistics" by Robert McCoy (Ballistics Research Lab Aberdeen Proving Grounds). The military abaandoned the use of ballistic coefficients in favor of measured drag data about 40 years ago. That's why you rarely see BC values published by the military. The whole concept of using ballistic coefficients is archaic. All they accomplish is to guarantee never having accurate trajectory calculations. With the invention of computers and millimeter wave doppler radar there's little excuse for not to having complete drag functions for every model of bullet manufactured. The use of G1 coefficients is mostly to help marketing. G1 coefficients are always much larger numbers and therefore more impressive than G7 coefficients, and drag tables are of little use except as computer files.
Who would buy a 30 caliber VLD bullet with a G7 BC .47 when they can have one with a G1 BC of .67? Sigh...
rooshooter
New member
Thanks for the info Louis. I wasnt thinking that the BC figures from sierra would be in G1, while the balistic program will be in G7, so as you say, G1 would be the one to use.
Mikecr, I have not shot at 1200 yds yet, only at 1000yds with another rifle. With this particular barrel I have a 800 meter scope setting, so I needed to work out how much extra to screw in for 1200, or whether I will need extra scope base inserts.
Mikecr, I have not shot at 1200 yds yet, only at 1000yds with another rifle. With this particular barrel I have a 800 meter scope setting, so I needed to work out how much extra to screw in for 1200, or whether I will need extra scope base inserts.
O
overbore
Guest
G-7
not the economic version, is under written current evaluation in Precision Shooting with a direct comparison published. I have gone to the updated data.
Cordially, Overbore
not the economic version, is under written current evaluation in Precision Shooting with a direct comparison published. I have gone to the updated data.
Cordially, Overbore