Range Report Ballistic FTE - Help!

[Chanonry]

Guys

I am confused. I am off to the range tomorrow first time out to 1000yds.

I have been running FTE which has worked well for me but this is a jump from about 500 to 1000 yards so I wanted to make sure that I had half decent models to get me in the ballpark.

I have a 168SMK load which seems to model fine but I also have some 200gr Accubonds. My problem is that there is a big difference between G1 and G7 models for this load - no surpises, but which is correct?

Intuitively the G1 model I ran gives the most 'sensible' profile but it is a BT so it should be G7?

I am using the JBM engine. What am I missing?

Andy

 

[Sniper1*]

Re: Ballistic FTE - Help!

Interested myself! I have not found any G7s to work in a program with my known data!

 

[deadly0311]

Re: Ballistic FTE - Help!

You may have some trouble reaching 1K with the 168 SMK, but i use the G7 BC, but if you can find the actual G7 BC by Bryan Litz that will be leaps and bounds better for you, the G7 for my 155 scenar was like 485 or something, but with Bryan's data of .274 G7 it almost matched my real world data perfectly. The FTE wont get you solid hits, but it will get you damn close.

G1 or Ingalls (by far the most popular)
G2 (Aberdeen J projectile)
G5 (short 7.5° boat-tail, 6.19 calibers long tangent ogive)
G6 (flatbase, 6 calibers long secant ogive)
G7 (long 7.5° boat-tail, 10 calibers tangent ogive, preferred by some manufacturers for very-low-drag bullets[10])
G8 (flatbase, 10 calibers long secant ogive)
GL (blunt lead nose)

To illustrate this a bullet manufacturer has published a G1 BC of 0.659 and a G7 BC of 0.337 for their 7 mm Match Target VLD bullet and has since published the G1 and G7 BCs for most of their target bullets. The last two snippits of info are from this

http://en.wikipedia.org/wiki/Ballistic_coefficient

 

[ReaperDriver]

Re: Ballistic FTE - Help!

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Chanonry</div><div class="ubbcode-body">Guys

I am confused. I am off to the range tomorrow first time out to 1000yds.

I have been running FTE which has worked well for me but this is a jump from about 500 to 1000 yards so I wanted to make sure that I had half decent models to get me in the ballpark.

I have a 168SMK load which seems to model fine but I also have some 200gr Accubonds. My problem is that there is a big difference between G1 and G7 models for this load - no surpises, but which is correct?

Intuitively the G1 model I ran gives the most 'sensible' profile but it is a BT so it should be G7?

I am using the JBM engine. What am I missing?

Andy </div></div>

I use G7 models almost exclusively for my 1K shooting and they've done very well with the Ballistic FTE/JBM combo on my iphone. But like anything... garbage in, garbage out. Make sure you have the correct G7 BCs but also have temps, baro pressure, MV all accurate for the shot. If any of those are off, your data is also going to be off at 1K. If you have accurate dope for several ranges at 500 yds and less, make sure it matches what you're getting from Ballistic FTE. If its not, most likely your MV is wrong. Play with the MVs in Ballistic until the output matches your dope and you're more likely to then be accurate at 1k.

2nd thing is my understanding is that G5 BC are probably more appropriate for the SMKs while the G7 are more for the longer VLD bullets. But my G7 has worked well so far with 175SMK and 178AMAXs, so I think it'll get you close.

Finally, the convential wisdom is that 168 SMKs are not great beyond about 800 yds due to them being a bit more unstable in the transonic range than other bullets. I know some guys say 168 SMKs shoot fine at 1K but they are in the vast minority, so don't be surprised if your 1K experience with them is squirrely.

good luck!

 

[azimutha]

Re: Ballistic FTE - Help!

Like Deadly said, get the more accurate G7 BCs from Litz' book. (It's well worth owning for the wealth of no-BS info on shooting). While other models, such as G5, might be a closer match sometimes, G1 and G7 cover most projectiles. In the book, he provides both at different velocities and you will also see an average as well as a variation number. Whichever model provides the lowest variation is the one to use. (Despite most of the bullets being boat tails or VLDs he measured some like the Nosler Partition and that is definitely one that fits the G1 model better).

In fact, out to 600 yards with many bullets, you will hardly notice a difference between drops using either model. But past that G7 will be more accurate (for bullets that fit that model). Again, the important thing is to get a more realistic BC in the first place (Nosler, as much as I like them, publish overly optimistic numbers). Then, as ReaperDriver mentioned, make sure the rest of your numbers are accurate.

 

[Supersubes]

Re: Ballistic FTE - Help!

Reading between the lines on your post, are you entering the actual G7's or are you simply switching the native drag model to G7(like .42 something with the program set to G7?). I have a friend who was doing that and he didn't understand why his G7 calculations were shall we say optimistic.

 

[Chanonry]

Re: Ballistic FTE - Help!

Guys Thanks for that. I now understand what I didn't know, which turns out to be quite a lot.

I had a laugh, it was blowing a bit way out there so we were scaring the target. Ironically the best hit was with a 158gr tracer I just lobbed down there for the hell of it without changing my dope. The one shot you don't expect to hit is sweet!

Andy

 

[One-Eyed Jack]

Re: Ballistic FTE - Help!

Cpl Snafu (aptly named) is worth rereading. If you want to use a G1 or G7 ballistic coefficient, make sure that FTE Ballistic knows which model you're using. You can't simply change the BC number -- you can't use the G1 drag model with a G7 BC (and vice versa), you will get erroneous results.