Range Report BC help

[earthquake]

This is a multi-part question. I currently use a ballistic program on my iPod called iSnipe. For the limited amount of shooting I do, it serves me well. However, it only allows input of one BC and one MUZZLE velocity. I use the G7 listed in Bryan Litz's book for 175 SMK's at 2,500 fps. at the muzzle. (my MV is 2,550 fps)

What program for iPods allow input of several BC's based on decreasing velocity at range? AND, has anyone noticed a large enough difference in come-ups to worry about it? What I'm getting at is, let's say the mil for 1k yards from iSnipe is -10.7 using only one BC. What would the drop be if I were to be able to input several BC for the velocity the bullet is traveling at 1k yards? Is the difference significant? Has anyone done this to compare?

I entered the BC for my MV and iSnipe gives 10.71 mils at 1k yards. When I entered the BC given in the book for 1,500 fps, but enter into iSnipe my MV of 2,550 fps, I got 10.69 mils for 1k yards...doesn't seem like much of a difference. But that's MV, not bullet speed at distance, so there's probably some error here?

MV=2,550fps (iSnipe), G7/BC=.243(2500fps book), Mil @ 1kyd = 10.71
MV=2,550fps(iSnipe), G7/BC=.246(1500fps book), Mil @ 1kyd = 10.69
MV=1,500fps(iSnipe), G7/BC=.246(1500fps book), Mil @ 1kyd = 31.35!
MV=2,550fps (iSnipe), G1/BC=.484 (2500fps book), Mil @ 1kyd = 10.74

I would like to see the difference, if any, between these results and those from being able to enter multiple BC for the slowing of the bullet at range. I use an FDAC too, and these numbers are somewhat similar. Real world results are different yet again, with me recording 11.0 mil at 1k when I was shooting at CRC. It's a 0.3 mil difference, or 10.8" which is significant.

Also, in reading Litz's book, on pg. 17 he shows a picture of Sierra's published BC for the 142gr 6.5mm match king bullet as .588 for 2,800fps+. That BC more closely resembles the G1 given later in the book, but that bullet looks like a G7 standard to me. The G7 given in the book is only .302 for that velocity. So my question for this part is, does it matter which standard G1/G7 I use in my program?

Sorry that this got long-winded!

 

[Lowlight]

Re: BC help

BulletFlight allows for banding your BC with multiple MVs and BCs.

The question is really not, "is there enough difference" when you change it from G1 to G7, the question is really, <span style="font-style: italic">"What is your actual Dope compared to the programs' solution" </span>

The BC you see .588 is G1, not G7, and it matters to some programs not all programs and if you step your BC and MV it matters even less, again, all that really matters is the solution and how close it matches your actual dope.

If you use the averaged G7 and you are within .3 mils at 1000 ok, but if you step G1 and you are within .1 than clearly you have a better predictor of the future. So you have to gather real world data and then see which software, G curve and method best serves you personally. There is no one right answer, it's a bit of trial and error.

If the system is calibrated, and the data entered is made to match your rifle under the current conditions chances are it will match or at least be closer throughout your shooting. If you allow it to be off, you'll always be off and how much will vary based on the factors inputted.

Computers are only as good as the data you feed it. Even then they are following a model based on a set of variables the programer wrote that he hopes will closely match a wide variety of rifles and shooters, he cannot predict how you shoot or with what you are shooting.

 

[earthquake]

Re: BC help

Thanks for the help. That clears up some misconceptions I've had with BC's. I sort of made my own "calculator" in Excel based off my real-world DOPE.

Vertical axis is mils, horizontal axis is range in yards. Red line is my DOPE from the CRC, blue line is my DOPE from the CD Combat Biathlon I shot, and the black line is my DOPE from a range day at the DOW range near Buena Vista.

I've been recording all my DOPE and putting it in Excel, then I used the trend-line function to get the equation for the slope of the line. I can then enter in the unknown variable (distance) into this equation and it spits out a mil value based off my data. Seems to work and was pretty easy to do once I got my own data.

Do you know how the FDAC's are created, i.e. which G-standard, BC they use and if it's stepped for distance? Thanks again.

 

[Lowlight]

Re: BC help

FDAC are G7 I believe ... I have no idea if they step it or average it, those guys are members here try emailing them.

The issue with the 308 is there is tons of data, real world and projected it is pretty hard to mess up with a 308. So almost everything is pretty darn close, certainly if you don't mess up the environmental data within 1 MOA or better. We just have too much data to really go wrong. It's pretty to get solid dope for it.

 

[earthquake]

Re: BC help

I see Bullet Flight lists three versions (military, L2 and L1). Would L1 be that much better than iSnipe, or should I go L2 or full Military?

Looking more for load development with a 6.5mm build I'm starting. Going to start reloading, thus have to play with powders, different bullet weights etc.

 

[Lowlight]

Re: BC help

If you are doing all that and you use Windows, get ColdBore, download and use it.

Coldbore is much more suited to development and using new / different bullet combinations.

It has both a Desktop feature and PDA combined for one price and the work done at the desk can talk to the PDA later. You can build cards, print DA stuff, etc, as well as analyze your data later on the computer.

Invest in Coldbore, buy a cheaper iPAQ PDA running Windows Mobile and stop worrying about whether an APP Is suitable... Coldbore is and does much more than any APP.