G1-g7?

[purdeydog]

G1 & G7 drag profiles


I'm sure there are several people on here who have a good understanding of this. I know what it means and how to use the data. What I can't find is good data on which profile to use when developing a good range card on a given bullet or caliber. Anyone know of any good data.


Now to my basic understanding at shorter distances there isn't a lot in it or if there is it's manageable. But with some ballistic profiles I've looked at for longer distances there is a huge difference in energy and velocity and when the bullet becomes unstable and the amount of drop, which affects which caliber I'm interested in getting as things get expensive quickly with the big calibers plus there's scope/moa adjustments to consider too.


Cheers

 

[bewsher500]

what bullet?

in my simple approach I use G1 on flat base hunting profile bullets and G7 on boat tail ballistic tipped ones with a higher calibre radius secant ogive (pointier!)

 

[Stacka]

I could blow your mind with G1-to G8 and the relevant ballistics.....but that's because i have no friends.

Long and short of it. as bewsher said above. G1 to G7 depending on the base.

But do understand the above gets affected by air density and velocity of the round, and alot more.

For what i imagine you would be doing you will need G7.

Finally you cant beat good data collection, real world data is the only true way to get it right, all i do now is make sure my loads are supper accurate at 100m (tightest group) then work out my BC at different ranges.

 

[purdeydog]

Thanks for the reply. The big calibers .338 and over are silly money so I don't really want to go there. I've been looking a lot at various .300 calibers or 7mm calibers and just can't decided want to get as the bullets and drag models vary so much. Ultimately I want a caliber to get me out to very long distances just for fun at the range. I've been looking at 7mm rem mag and 300 win mag. Both rifles and cartridges seem available, not too costly. However when I look at there Characteristics it all depends on what drag profile your using with the right bullet. For example a 300wm with 195g Hornady BTSP hits the transonic area about 1400y on G1. Change that to G7 and your good for 2000y plus.

 

[purdeydog]

Thanks Stacka. I too wish to lose all my friends and Find some real world data. Yes I been looking at all the variables needed to take into account, the weather, spin drift etc, working out my calculation and so on. I would enjoy developing a chart.

 

[Vipa]

Thanks for the reply. The big calibers .338 and over are silly money so I don't really want to go there. I've been looking a lot at various .300 calibers or 7mm calibers and just can't decided want to get as the bullets and drag models vary so much. Ultimately I want a caliber to get me out to very long distances just for fun at the range. I've been looking at 7mm rem mag and 300 win mag. Both rifles and cartridges seem available, not too costly. However when I look at there Characteristics it all depends on what drag profile your using with the right bullet. For example a 300wm with 195g Hornady BTSP hits the transonic area about 1400y on G1. Change that to G7 and your good for 2000y plus.

If you want distance, accurately without going for military sniper calibres, look at 6 & 6.5mm.. there is a reason why most bench rest shooters use them! Much more aerodynamic than 7mm+ lumps.. ok.. they won't arrive at their destination with the same amount of energy but unless you are shooting living things or want material destruction at extended range then it is of no consequence.... AND.... I can tell you from personal experience of shooting many a long range F/tr comp, that less recoil = a lasting hobby and much less pain and discomfort... big calibres are fine if in a fire trench or standing... you can absorb the recoil... try it prone and it just equals misery... even my .308 TRG... prone over a 50 round 1k comp... I couldn't touch the bruise on my shoulder for a week (and no, there is nothing wrong with my technique.. when prone, the only things that absorb the recoil are your collar bone and the thin tissues around it!!!!) 6mmbr & the 6.5 family give almost the same trajectory as a .338 Lap Mag.. with a fraction of the recoil... in other words, shooting them over extended periods, even prone, is fun and not a pain... The guys that turn up to the range with their 300 Win & Wetherby Mags etc.. put a couple of rounds through them and put them away!!!

If you want to end up not shooting... get a 300 magnum! if you want to enjoy your shooting, get something sensible!

 

[jthyttin]

However when I look at there Characteristics it all depends on what drag profile your using with the right bullet. For example a 300wm with 195g Hornady BTSP hits the transonic area about 1400y on G1. Change that to G7 and your good for 2000y plus.

Ehh, where did you get G7 BC for Hornady 190gr BTSP, which I assume you're talking about? BTW it's discontinued. You cannot just use G1 BC and G7 function.

I looked at JBM (http://jbmballistics.com) and the Litz derived G7 of 0.238 is actually worse than Hornady stated G1 of 0.491. I had to push the muzzle velocity (at sea level) to 1000m/s to get 340m/s at 1400y (G1). With G7 the velocity drops below 340m/s before 1300y.

 

[bewsher500]

Ehh, where did you get G7 BC for Hornady 190gr BTSP, which I assume you're talking about? BTW it's discontinued. You cannot just use G1 BC and G7 function.

I looked at JBM (http://jbmballistics.com) and the Litz derived G7 of 0.238 is actually worse than Hornady stated G1 of 0.491. I had to push the muzzle velocity (at sea level) to 1000m/s to get 340m/s at 1400y (G1). With G7 the velocity drops below 340m/s before 1300y.

That is standard
difference is one is a marketing tool by the manufacturer and one is an independent assessment of real world results


http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA554683

 

[purdeydog]

Hi thanks for the replies. Yes I know you can't just use any old profile. That was the whole of point of my post, where can I find good data on which profile to use on which bullet. All of the online or app ballistic calculators give you the option to decide which one to use. I don't know which one to use, im trying to decide on what rifle I want to get for my little long range project. I don't want to buy a rifle that won't have bullets for what I want. The Hornady 195btsp was an example from Ballistic AE, who by the sound of it are using old data. On the Hornady website that bullet is there, they state that's a boat tail design bullet, which would be a G7 profile but I could well be wrong. Thanks.

 

[jthyttin]

Just forget the profiles and use JBM Simplified Trajectory with bullets from library (dropdown menu). Then BC and G function will be automatically matched.

In library there's several entries for some bullets. Entries G7, Litz and CD (Lapua data) are very accurate. Ideally you'd like to compare only those, if applicable.

http://jbmballistics.com/cgi-bin/jbmtraj_simp-5.1.cgi

 

[purdeydog]

Nice one thanks guys.