Thanks

- Thread starter TheDavidKemp
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Thanks

- Oct 17, 2018

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It also depends on what distances your using them at.

1000 yards and in I’ve found all the common bullets I’ve used BC’s to be easily close enough.

After 1200 all of them need adjustments even Hornandy’s 1.75 Mach numbers.

I think their prices are more impressive than the Bc’s.

BC numbers are fluid, dynamic in fact and will change from system to system, rifle to rifle.

As an example using 6.5 PRC 147 ELD-M, Hornady has 3 BC bands:

Mach 2.25 = 0.351 G2

Mach 2.0 = 0.332 G2

Mach 1.75 = 0.321 G2

What is the correct way to use these values for a bullet starting at Mach 2.5 and ending at, say Mach 1.9?

Here are a few ways to calculate:

1) As bullet drops from Mach 2.5 to Mach 2.1, use 0.351 G2, then as bullet drops from Mach 2.0 to Mach 1.9, use 0.332 G2

or

2) Since ending velocity is Mach 1.9, just use 0.332 G2 across the whole range from Mach 2.5 to Mach 1.9

or

3) Use linear interpolation each step along the way to average out the BC from Mach 2.5 down to Mach 1.9 using both 0.351 G2 and 0.332 G2

Thanks.

I have to change the way I think about these things. Using the numbers given as a reference. I'm trying to decide which weight class bullet to go with, 130/140/147/153-156.

Shooting a 26" krieger in 6.5 creed and wanting to stay around that 2850 line because I do use this rifle as a hunting rifle for eastern whitetail and western big game so carried energy is important.

Whats better: pushing a 130 to 2900+ or a ride a slow 156 and get what I can? Im basically trying to get a grasp on what numbers I can actually get from a 130 or 156.

I used the 1.75 Mach value to 1200ish comfortably.

As an example using 6.5 PRC 147 ELD-M, Hornady has 3 BC bands:

Mach 2.25 = 0.351 G2

Mach 2.0 = 0.332 G2

Mach 1.75 = 0.321 G2

What is the correct way to use these values for a bullet starting at Mach 2.5 and ending at, say Mach 1.9?

Here are a few ways to calculate:

1) As bullet drops from Mach 2.5 to Mach 2.1, use 0.351 G2, then as bullet drops from Mach 2.0 to Mach 1.9, use 0.332 G2

or

2) Since ending velocity is Mach 1.9, just use 0.332 G2 across the whole range from Mach 2.5 to Mach 1.9

or

3) Use linear interpolation each step along the way to average out the BC from Mach 2.5 down to Mach 1.9 using both 0.351 G2 and 0.332 G2

Thanks.

The other Mach values are for closer targets.

I made a custom BC using all three but it didn’t jive to actuals as well as a straight 1.75 Mach BC.

To get it to true to a mile I’m using a .308 BC with a slight FPS tweak.

It’s not perfect but it’s close enough.

I’m sure I could sit down and hash out a custom BC on ballistic AE or AB for my bullet and barrel combinations I tried 4dof and with a bit of fiddling with the form factor it’s almost perfect.As a further example, StrelokPro has a multi-BC input function. I really wonder the various ballistic apps takes into proper account how Hornady uses these BC bands, or how it should be used to properly calculate a correct BC value. Because back to the OP's question, if we are inputting or using these BC bands incorrectly at various distances, or if the app is not using these BC bands correctly, we have only ourselves to blame when the trajectories don't line up.

Poof.

I’d rather be shooting, reloading or looking at porn than fiddling with numbers for an hour or two.

Now I just dream about a ballistic AE app with 4dof built in.

Yup and if you use the 4Dof with the custom curves there is no need to even worry about the BC. Been using 4Dof all year and it's very accurate. I haven't had to mess with anything. Put in the info and it's on.

I think their prices are more impressive than the Bc’s.

I'm not asking to be told what to do, I just want to have information laid out in a manner I can understand and make my own decision. But I feel like I'm on the brink or past the point of splitting hairs.

Thanks again everyone for input and clarification.

So try to balance both so they work out in your favor,

You are.I feel like I'm on the brink or past the point of splitting hairs..

Go shoot. The bullet tells the truth.

But I haven't been able to find any documentation on how to do this. 'Twould be nice to know.

Been offline/off range since December due to health. I had started a load development for the 260/143ELD-X/H-4350, and intend to pick it back up this Fall. I suspect it'll be particularly good, especially at my medium altitude of 4350ft ASL.

I found pressure early, so I'd strongly suggest starting fairly low and working on up with this particular bullet; I suspect the longer bearing surface is involved. There were other issues with the rifle (I.e. short headspace), and the solution still needs to be proven; but everything is precisely correct by the gauges/numbers now. All of my 260 and 308 dies and chambers are set up to coincide with the same 308 case gauge and headspace gauge; SAAMI all the way.

Greg

I found pressure early, so I'd strongly suggest starting fairly low and working on up with this particular bullet; I suspect the longer bearing surface is involved. There were other issues with the rifle (I.e. short headspace), and the solution still needs to be proven; but everything is precisely correct by the gauges/numbers now. All of my 260 and 308 dies and chambers are set up to coincide with the same 308 case gauge and headspace gauge; SAAMI all the way.

Greg

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