...My understanding, and the way I use ballistic apps, is any published or reported BC are a starting point. The proper thing to do is to get your rifle/bullets actual drop at a variety of ranges. Then use that data to tweak the ballistic software so it will then calculate accurate adjustments based off of your bullet and velocity setup.
My experience has been the published numbers are close enough to be useful at sub 800 yards (sometimes less sometimes more) and then I tweak based off of actual results and can reach out further as desired and tweak more until I'm happy with the software calculations.
BC is not static, it changes with velocity/temperature or Mach#. It can vary in different rifles. The best is to use a solver with a doppler reading for the bullet throughout its trajectory for your rifle, or different BCs as the bullet slows through the flight path. If not, your SIG uses Applied Ballistics library which is a well-tested value to start with and then true your data at distance. Make sure your zero is dead-nuts perfect.
This. You're going to need to validate this in your own rifle with your loads. The posted BC will get you close to start with. I don't have a Sig but hopefully you can "true" it to match your validated drops.
My 6.5 Sherman Max validated very close to the stated .347 G7...
Dang.....I wanted to answer this one! It makes me feel.smarter than I actually am when I explain B.C. as a dynamic number, versus the static number that many think that it is. This advice is spot on!
This topic is something that gets me a little riled up, so pardon the impending rant (and consider I'm talking about LRH, not ELR target shooting)...
I personally think this is used as an excuse by bullet manufacturers to justify inflated B.C. values. I've "verified" a couple of dozen different bullets using a LabRadar, and have fired many thousands of dollars of lead at targets near and far in quite a few different barrels and calibers from 10° to 100°. Berger and Hornady B.C. values do not vary more than about 3% from their stated values, and in a few cases are
higher than quoted by a bit. I've yet to find any other maker who's B.C. came in higher than quoted, which would be the case if the data was just random "variation" from rifle to rifle...
Take it for what it's worth, but here's my list of reasons that "verify for yourself because all rifles are different" is a problematic answer for hunters who are shooting at 100-1000 yards, and is unreasonably putting the burden of proof on the consumer, which allows manufacturers to basically lie at will...
1) Few shooters will have the resources, skills, and time to properly verify a B.C., and in some cases do more harm than good, because...
A) It requires multiple variables to be accurately recorded (e.g. Temp, pressure, range, wind, muzzle velocity), which require somewhat expensive equipment and careful methodology.
B) It requires a large number of shots at a variety of ranges, even if you own one of those elusive "half MOA all day" rifles I hear about on the interwebs. It's enough shots that the rifle condition can actually change throughout the course of verifying the B.C. for a bullet (i.e. heat and fouling).
C) It requires a very precise zero, which also needs precise variables recorded and accounted for at the time of zeroing (e.g. T/P, range, muzzle velocity, and wind) vs the time of B.C. verification.
2) G7 B.C. does not vary appreciably with mach number within typical hunting range velocities (e.g. 2000 - 3000 fps). G1 B.C. is more variable, but still not hugely so unless you are approaching the end of long range hunting distances.
3) Twist rate does not affect B.C. nearly as much as some would suggest, unless your system is already marginally stable. Most rifles and bullets are already optimized for one another, so this is rare for the normal hunter, and folks looking to run the real "long and heavy" stuff are likely already aware of this, and/or the manufacturers already state a "recommended twist". In short, twist is unlikely to affect B.C. unless you're in an odd situation you probably shouldn't be in...(looking at you 1:14 twist 22-250...
)
4) If you are lucky enough to have a LabRadar, and the ability to use it effectively, and enough time and money to shoot real far a lot, you discover that all manufacturers are inflating their B.C. values to some degree, though Hornady and Berger seem to be dang near "honest".
5) I've run the LabRadar for the same bullet across multiple rifles with different twists and velocities on a few occassions, and the numbers are always within a percent or so. In my testing, B.C. will vary from shot to shot or rifle to rifle no more than about 2%. That's a whopping 1/4 MOA difference at 1000 yards. One scope click. Way less than a 10 yard range error, less than a 45° wind direction change from aerodynamic jump, less than a 10° uphill incline, less than a 20 fps velocity difference, less than...Sorry...you get the point...
In summary, we are out here "verifying B.C." because manufacturers are lying to us, but love to hide it behind the "common knowledge" excuse that "all rifles are different"...
