dskinsler83 Posted March 11, 2012 Share Posted March 11, 2012 Which drag model is the SMK 175gr HPBT in a ballistic program? G? Link to comment Share on other sites More sharing options...
lee blackman Posted March 11, 2012 Share Posted March 11, 2012 (edited) If your looking at something around .495 or .505 over 2800fps that is the G1. It will work. The G7 is .243 i think and might be a more accurate profile if your program gives you the option to use it instead of the G1. As far as I understand G1 is the generic, and works for just about any rifle bullet, but you will get a more accurate trajectory estimate with the G7 on a boat tailed match bullet. Edited March 11, 2012 by lee blackman Link to comment Share on other sites More sharing options...
bgary Posted March 11, 2012 Share Posted March 11, 2012 The G1 drag model uses a "standard projectile" that matches the Ingalls tables (observed data). It's the one that Sierra uses in their data, but it isn't a very good fit for modern projectiles. The G7 drag model uses a "standard projectile" that has a shape very similar to modern bullets - long nose and boat tail - so it more accurately reflects the drag characteristics for that kind of bullet. Either one will work, but the G7 will be more consistent across a range of velocities Link to comment Share on other sites More sharing options...
The Surgeon Posted March 11, 2012 Share Posted March 11, 2012 (edited) What software are you using? As long range precision shooting continues to catch on, many software developers are offering the user a choice in the two models. +1 to Jakers. Edited March 11, 2012 by The Surgeon Link to comment Share on other sites More sharing options...
Graham Smith Posted March 11, 2012 Share Posted March 11, 2012 Which drag model is the SMK 175gr HPBT in a ballistic program? G? Depends on the program. AFAIK, most use the published G1 values. If you are using the JBM web site and you choose a bullet with the word (Litz) after it, that's using the G7 values from Brian Litz's book. Link to comment Share on other sites More sharing options...
dskinsler83 Posted March 11, 2012 Author Share Posted March 11, 2012 JBM mobile app Link to comment Share on other sites More sharing options...
Graham Smith Posted March 12, 2012 Share Posted March 12, 2012 JBM mobile app Ballistic FTE is rather confusing. It allows you to pick a profile and the drag model and it shows the BC's it's using, but even if I specify G7 it's showing me G1 BC's for my projectile. So I really don't know what it's doing. So, I created my own profile using the G7 drag model BC's from Litz. I'm still not sure if one is more accurate than the other and won't until I get a chance to shoot at 800-1000yds and compare. Link to comment Share on other sites More sharing options...
kevinj308 Posted March 13, 2012 Share Posted March 13, 2012 Check this out http://bulletin.accurateshooter.com/2012/02/g1-vs-g7-ballistic-coefficients-what-you-need-to-know/ Link to comment Share on other sites More sharing options...
Graham Smith Posted March 13, 2012 Share Posted March 13, 2012 Check this out I've seen that. Doesn't mean I really understand it. I understand that G7 is better than G1 for most long range HPBT bullets today, but you still have to know what the G7 BC's are in order to use them. If you use the JBM calculator and give it a G1 BC but tell it to use a G7 calculation, it's going to think that the number you have give is a G7 BC and your results are going to be way off. There's also the difference between the MFG values and the Litz measured values. For example, for my bullet (Sierra .308 155gr Palma 2156): Mfg G1 0.504 @ 2700fps Litz G1 0.442 @ 2700fps Litz G7 0.217 @ 2700fps Further, the BC goes down as the velocity goes down, so programs that use a variable calculation will give you a different value than those that don't. I've found that most of this stuff makes more sense after a couple beers. Link to comment Share on other sites More sharing options...
kevinj308 Posted March 13, 2012 Share Posted March 13, 2012 Seems like you understand pretty well. Must have been the beer! Always helps me too Link to comment Share on other sites More sharing options...
Graham Smith Posted March 13, 2012 Share Posted March 13, 2012 Of course, all of this is just an estimate anyway. There's no substitute for bullets on paper at various distances, temps, and altitudes. A log book you build yourself will always be more accurate. Link to comment Share on other sites More sharing options...
usmc0326 Posted May 3, 2012 Share Posted May 3, 2012 Which drag model is the SMK 175gr HPBT in a ballistic program? G? G1 drag model is for bullets that are square base (the name eludes me at the moment), the G7 scale are for your VLD / boat tail bullets. Link to comment Share on other sites More sharing options...
Seekins Posted May 9, 2012 Share Posted May 9, 2012 Your environmental info will throw you off more than anything else. Start with g1, known velocity and bc. Shoot your gun past 700 yds and see how close you are. get real data then see what model is closer. I shoot at 500, 700 then 1200 to test data. If it works out at those 3 distances your good to go. If not then check enviorment data first, then fudge velocity and bc until it works out to what your actual bullet is doing. I use G1 with 115 dtac bullets and my data Is perfect. Link to comment Share on other sites More sharing options...
hrt4me Posted June 13, 2012 Share Posted June 13, 2012 Your environmental info will throw you off more than anything else. Start with g1, known velocity and bc. Shoot your gun past 700 yds and see how close you are. get real data then see what model is closer. I shoot at 500, 700 then 1200 to test data. If it works out at those 3 distances your good to go. If not then check enviorment data first, then fudge velocity and bc until it works out to what your actual bullet is doing. I use G1 with 115 dtac bullets and my data Is perfect. perfect? to 1200 yards? Link to comment Share on other sites More sharing options...
Stlhead Posted June 13, 2012 Share Posted June 13, 2012 Don't listen to that Glen guy, he does not know what he is talking about. Only T-baggers use the DTAC, all the cool kids are using the new 105 hybrids. I have found that the G7 model and Litz values seem to more closely conform to the path my bullets take, but you need to verify whatever info you get from a ballistic modeling program with actual verified field observations. Use whatever model, program or values that will most consistently give you the data that your range sessions confirm. It is impossible to actually shoot groups at every range imaginable, so you need to find a model that can fill in the blanks from the data you input, and matches your actual verified drops at the range. While I do not have a good 1200 yard range, I do shoot at 1000 yards on a regular basis, and confirm my dope at 500 880 and 1000 (there are Silhouette chickens at 880 at one of the ranges I frequent) if you dope is good enough to hit a chicken at 880 it will be good enough to do well at most matches. I was being sarcastic about Glen, he is a very accomplished long range competitor, and a great guy. When he offers advice about shooting rifles it would be wise to heed it. Cheers! Link to comment Share on other sites More sharing options...
Graham Smith Posted June 14, 2012 Share Posted June 14, 2012 Start with g1, known velocity and bc. Shoot your gun past 700 yds and see how close you are. get real data then see what model is closer. FWIW, a few weeks ago I had a chance to test out my 155gr .308 load at distances from 100 to 1000+ yds. What I found is that no matter what model I used, the calculated values were off by enough to make a difference. Ultimately G7 with an altered velocity ended up being the closest. I can now be fairly confident that as long as I have a reading of temperature and absolute pressure, I've got a reasonably accurate set of data out to 1100 yds for my load in my gun. But I would not guarantee that someone else would get the same results. Link to comment Share on other sites More sharing options...
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