Ballistics calculator--help with terminology?

[Monkeyleg]

I downloaded a ballistics calculator for my mobile phone, more out of curiousity than anything, as I don't know of anywhere nearby to shoot long range.

In trying to figure this out, there's a few terms I don't understand, and don't know what values to plug in. I'm trying to get an idea of numbers for .308, with 2800 fps at the muzzle, zeroed for 100 yards, 168 gr Sierra HPBT (drag coefficient I think is .48).

Anywho, the calculator requires entering a break velocity number, and what's abbreviated as retard. coeffienc. rate. I don't know what these are, although I'm getting a vague idea from searching.

Can anyone provide stand-in values for these, or explain how to arrive at the correct numbers?

Thanks for any replies.

 

[Lovesbeer99]

The devleoper should be able to provide a user guide defining all the fields.

Which app is it?

 

[rattletrap1970]

I'd check with the developer of the software as they may not be using standard terminology.

 

[Dave P]

retardant coefficient rate?? Sounds like a function of the powder.

Programs like Quickload know all those details when you tell it you are using IMR4064, etc.

 

[C Broad Arrow]

I downloaded the same program for my BB 9800 and was wondering the same thing.
Any help here would be appreciated. I also have sent a note to the developer asking for an explaination.

 

[Hud]

I have a Pejsa Ballistic Calculator spreadsheet that I used to use quite a bit before I got programs that do all the calculations automatically.

It also has inputs for retard coef. rate & break velocity (fps).
Notes in the sheet indicate that the retard coef. rate is based on whether the bullet is boat-tail or flat base (difference in drag on the base of the bullet) & recommends a value of 0.50 for boat-tail Spitzer bullets & 0.40 for flat-based bullets.

The notes also state that predictions are not precise for bullet speeds below trans-sonic Break Velocity which it recommends as 1300 fps for most rifle bullets.

When I use the spreadsheet, I leave the break velovity at 1300 & change the retard coef. for either a boat-tail or flat-base bullet.
These values will have a greater affect at long ranges than at short ranges like 100 yds.

Regards, Hud

 

[taliv]

not a direct answer to your question, but pre-answering your next few questions read this: http://www.arcanamavens.com/LBSFiles/Shooting/Downloads/Programs/

 

[HKGuns]

Hitting 1.7" high at 100 yards will get you in the ballpark for most 150 & 165 grain loads for a 200 yard zero, which is most common for that round.

 

[Monkeyleg]

Thanks for the replies. It seems like those two values can be left where they are without affecting things a lot, but it still was bugging me, so I did more digging.

Taliv, the link you provided talks about variations in ballistic coefficients at different ranges. I've read about this in long range hunting forums, and I think that may be what the reference to "retard. coefficien. rate" may be. There may be way to come up with a value that factors in the variation of the BC of a bullet the further out the target.

Near as I can tell, break velocity has something to do with the speed at which a bullet transitions from super-sonic to sub-sonic, which apparently can vary by the bullet design. That would explain the 1300 number that Hud is referencing.

This is much more information than I need, and much more complex than I need. I'm just always fascinated by something that I can't find by searching on Google, Bing or Yahoo.

 

[Cemetery21]

Try this one - inputs are more intuitive.

http://www.handloads.com/calc/

Regards, Jim

 

[Monkeyleg]

Thanks, Jim. I've seen a few like that one, but it's simple enough that it would load quickly on a Blackberry. Similar calculators on other websites load slowly because of the website's graphics.

I don't need the complicated one, I'm just trying to figure out what those values mean. If I ever get to shooting at over 300-500 yards, maybe I'll need the complicated one.