Hello,
So, I am trying to expand my horizons to some longer distance precision shooting. Im moderately experienced out to 500 yards, but have had very little opportunity until now to shoot farther. I figured the first place to start is to upgrade my equipment and build a good ballistic card. I have recently ditched my Millett LRS-1 and have stepped up to a Bushnell XRS (love it).
I did some OCW development and found a nice load for my .308. 3/8th -5/8th MOA consistantly. Extreme Spread of 15 FPS over 20 shots. 2643 FPS mean velocity.
I used JDM ballistics to build this little table. Cut it down to size and it fits well in my pocket with my book and calculator. The gray adjustments are based off of powder and atmospheric temps @ 29.92 inHg. The tan data is my "barometric modifier" which was configured at 60* F. The percentages listed under the pressures (in tan) are percentage modifiers that are meant to applied to the wind data.
So... check my logic. Lets say I was calculating a firing solution at 1000 yards for a 30*F day, at 28inHg, 10*downhill, 7mph Crosswind at 60* left.
Elevation Logic:
(1000 x .984(cosine of angle))= 984 yards.
984>> U10.9 MILS -.5MILS (baro value) = U10.4 MIL
Windage Logic:
-.3 (spin) + (2.9 x .7(speed) x .91 (baro) x .9(angle)) = ~1.4 RIGHT
Anyone finding anything suspect with this method? It checks out pretty close to the JDM ballistics. I just want to make sure im not making any theory errors.
Any idea, suggestions or critiques for my card?
Thanks fellas,
Bryson
So, I am trying to expand my horizons to some longer distance precision shooting. Im moderately experienced out to 500 yards, but have had very little opportunity until now to shoot farther. I figured the first place to start is to upgrade my equipment and build a good ballistic card. I have recently ditched my Millett LRS-1 and have stepped up to a Bushnell XRS (love it).
I did some OCW development and found a nice load for my .308. 3/8th -5/8th MOA consistantly. Extreme Spread of 15 FPS over 20 shots. 2643 FPS mean velocity.
I used JDM ballistics to build this little table. Cut it down to size and it fits well in my pocket with my book and calculator. The gray adjustments are based off of powder and atmospheric temps @ 29.92 inHg. The tan data is my "barometric modifier" which was configured at 60* F. The percentages listed under the pressures (in tan) are percentage modifiers that are meant to applied to the wind data.
So... check my logic. Lets say I was calculating a firing solution at 1000 yards for a 30*F day, at 28inHg, 10*downhill, 7mph Crosswind at 60* left.
Elevation Logic:
(1000 x .984(cosine of angle))= 984 yards.
984>> U10.9 MILS -.5MILS (baro value) = U10.4 MIL
Windage Logic:
-.3 (spin) + (2.9 x .7(speed) x .91 (baro) x .9(angle)) = ~1.4 RIGHT
Anyone finding anything suspect with this method? It checks out pretty close to the JDM ballistics. I just want to make sure im not making any theory errors.
Any idea, suggestions or critiques for my card?
Thanks fellas,
Bryson