When using a Sierra HPBT match king. Would one use a G-5 drag table or the standard G-1. I'm playing around with RSI and infinity RSI offers the option to change drag table. Also Pressure?? What is this and what numbers go into that area? I understand altitude Humidity temp etc. Pressure? Thanks in advance Joe

Heeeeey Joe, whatcha doing with that gun in yore hand ,da duun da duun da dunn dunn /ubbthreads/images/graemlins/grin.gifSorry Joe , could'nt resist that opportunity. All the recent info I've been reading including that coming from Sierra indicates the G1 drag function is best suited for all applications tthat would apply to the reloader. As always there is probably more to it than that . Jim

Let me see if I can illustrate this. The drag of the bullet (using the ballistic coefficient and drag function model) is proportional to the drag function divided by the ballistic coefficient (among other things). This means as the BC goes up, the drag drops. Since you have two numbers to play with, the drag function value and the BC value, there are many combinations that give you the same drag value. For example, you can use the G1 drag function and a G1 BC or you can use the G7 (or G5, or G8...) drag function and a G7 BC. As long as you use the BC developed for the drag function you get the right answer -- that's the key. Look at the following data calculated for the 210 grain Berger VLD: Vel. G7 G1 1500 0.327 0.590 1600 0.320 0.600 1700 0.317 0.612 1800 0.316 0.621 1900 0.316 0.626 2000 0.316 0.630 2100 0.316 0.633 2200 0.317 0.636 2300 0.318 0.638 2400 0.319 0.640 2500 0.321 0.643 2600 0.322 0.647 2700 0.324 0.651 2800 0.326 0.656 2900 0.328 0.663 3000 0.330 0.670 3100 0.332 0.677 3200 0.333 0.686 3300 0.335 0.695 3400 0.337 0.705 3500 0.338 0.715 It is two ballistic coefficients as a function of velocity for two different drag functions. If the drag functions fit the bullet perfectly, the number would the same for all velocities -- that's the point of the ballistic coefficient -- one number instead of having to remember and implement many different coefficients. Now when you look at the data above, which coefficient comes closer to the ideal, the G7 or the G1? Obviously the G7 fits better because it varies from 0.327 to 0.338 (difference of 0.011) compared to the G1 change of 0.125, more than 10 times as much. Now ask yourselves which BC the bullet manufacturers would rather list. Would they rather publish 0.330 or 0.670? Of course they're going to publish the 0.670 because it sounds better and many people don't understand what it all means. So we're stuck with multiple ballistic coefficients as a function of velocity to make up for the short comings in the drag function. We could easily use a single number if we used the G7 drag function. To make it worse, many programs don't (or didn't) allow you to pick your drag function. So, if you're using BCs published by Sierra, use the G1 drag function or you'll get huge errors. Brad P.S. I would assume the pressure is atmospheric pressure used in the air density calculation. Now whether it is absolute or corrected, I couldn't tell you.

Outstanding...Man, that makes perfect sense now...Yes, I had to read it several times /ubbthreads/images/graemlins/wink.gif BTW RSi seems to make the adjustment for the other drag tables. BAd thing about RSI is I cant really take it with me. I have a pocket PC and workin off that. Hmmm..Maybe exbal? Right now I'm using "the Thing" as well as Steve Klinkers software Beta. It actually works pretty good Joe Thanks Joe