Im shooting a 260ai 2950fps 139gr lapua scenar .615bc. Iam shooting 500-600yards at the range and upto 1000 yards -.When I enter my figures into exbal I enter a single starting BC of .615 for my drop.I have recently been shown the light that this single BC entry is not satisfactory as obviously the bc changes with the speed and time of flight of any given projectile .I have used the pejsa online caculator and compared with exbal at 500 yards.Pejsa has a BC retardation figure built onto this programe -not that I really know how to use its super scientific calculation areas well.The figures are slightly different with these 2 programes .Can any one help me with how to find my altering bc through the different ranges -some caculation or some exitisting info ?Will the difference with one BC over multiple BC caculations change the bullet impact drastically at 1000 yards
Range Report mutiple BC,s effect
Re: mutiple BC,s effect
ch'e,
Here are your options for calculating a proper trajectory for that bullet using the different programs. The BC's I'm listing were measured experimentally with a process that's repeatable within +/-1%, and are in near perfect agreement with Lapuas doppler radar data.
1. Using a standard ballistics program that accepts a single G1 BC, use the average G1 BC of 0.557. This is the average G1 BC from 3000 fps to 1500 fps.
2. Using the Pejsa program that 'erodes' the high velocity BC, use 0.598 as the G1 BC at high speed (3000+ fps).
3. Using multiple G1 BC's, you can enter the following:
0.598 above 3000 fps
0.586 from 3000 fps to 2500 fps
0.565 from 2500 fps to 2000 fps
0.528 from 2000 fps to 1500 fps
0.499 below 1500 fps
4. Using a program that accepts BC's referenced to the G7 standard, you can use a G7 BC of 0.285 which is valid for all speeds.
All 4 of the above approaches should produce similar trajectories.
Note: The 139 Scenars that I tested for BC had slightly larger than average tip diameters (about 0.076" wide). If your bullets have smaller tips, like a more average 0.060" to 0.065", you can add about 2% to all of the BC's given above.
I'm curious to know how the above calculations line up with each other and with your observed results.
-Bryan
ch'e,
Here are your options for calculating a proper trajectory for that bullet using the different programs. The BC's I'm listing were measured experimentally with a process that's repeatable within +/-1%, and are in near perfect agreement with Lapuas doppler radar data.
1. Using a standard ballistics program that accepts a single G1 BC, use the average G1 BC of 0.557. This is the average G1 BC from 3000 fps to 1500 fps.
2. Using the Pejsa program that 'erodes' the high velocity BC, use 0.598 as the G1 BC at high speed (3000+ fps).
3. Using multiple G1 BC's, you can enter the following:
0.598 above 3000 fps
0.586 from 3000 fps to 2500 fps
0.565 from 2500 fps to 2000 fps
0.528 from 2000 fps to 1500 fps
0.499 below 1500 fps
4. Using a program that accepts BC's referenced to the G7 standard, you can use a G7 BC of 0.285 which is valid for all speeds.
All 4 of the above approaches should produce similar trajectories.
Note: The 139 Scenars that I tested for BC had slightly larger than average tip diameters (about 0.076" wide). If your bullets have smaller tips, like a more average 0.060" to 0.065", you can add about 2% to all of the BC's given above.
I'm curious to know how the above calculations line up with each other and with your observed results.
-Bryan
Re: mutiple BC,s effect
I couldnt have had a better reply from a more qualifies person -your fantastic Bryan!!! cheers
I couldnt have had a better reply from a more qualifies person -your fantastic Bryan!!! cheers
Re: mutiple BC,s effect
Now I have got my BCs sorted I am left with another question -139 lapua scenar using retarding BCs in demonstration 3 above with speed of 2870fps well two questions--if my elevation is 27.56 at 1000 yards and my latitude is 36-57degs shooting east with 2.62 drop due to coriolis
my math is (flight time 1.42 sec) x (coriolis 2.62) =3.72inchs low east -x (cosign of latitude 36.57=.8031) x (3.72 low east) =2.98 inchs to take off my original elevation? 2NDquestion Would be the horozontal movement with no wind results in around an 8-9 inch right hand movement in the Northern hemisphere but 1/2 that down under say 4 to 4.5 inches due to gravity pushing the oppersite direction than the northern Hem. -- what coriolis affect would one add to this southern situation for side ways drift ??Gee I hope that makes sense
Now I have got my BCs sorted I am left with another question -139 lapua scenar using retarding BCs in demonstration 3 above with speed of 2870fps well two questions--if my elevation is 27.56 at 1000 yards and my latitude is 36-57degs shooting east with 2.62 drop due to coriolis
my math is (flight time 1.42 sec) x (coriolis 2.62) =3.72inchs low east -x (cosign of latitude 36.57=.8031) x (3.72 low east) =2.98 inchs to take off my original elevation? 2NDquestion Would be the horozontal movement with no wind results in around an 8-9 inch right hand movement in the Northern hemisphere but 1/2 that down under say 4 to 4.5 inches due to gravity pushing the oppersite direction than the northern Hem. -- what coriolis affect would one add to this southern situation for side ways drift ??Gee I hope that makes sense
Re: mutiple BC,s effect
ch'e,
I've posted some worked examples of how to calculate Coreolis deflection in the horizontal and vertical planes on my website. You can get to the pages by going to the gyroscopic and coreolis drift link and scrolling down to the bottom.
Here are the shortcuts:
Horizontal
Vertical
-Bryan
ch'e,
I've posted some worked examples of how to calculate Coreolis deflection in the horizontal and vertical planes on my website. You can get to the pages by going to the gyroscopic and coreolis drift link and scrolling down to the bottom.
Here are the shortcuts:
Horizontal
Vertical
-Bryan
