Ballistic Coefficient.....? Looking for an easy read

[Dan-o]

There was a thread from a forum member asking which caliber to use for wolf.

I went with 25-06, but he said they don't have flat shooting bullets.   He referenced that 6 and 6.5's rule the long range games.

I'm sure he's right - and I didn't want to thread jack him - but it got me to wondering why a 6 or 6.5 would fly flatter than a 25.

Any good reads out there that explain ballistic coefficient, sectional density and anything else that contributes to making bullets fly flat?

thx,

Dan

[2labs]

Shhh. 25-06= 6.5mm

[slm9s]

It doesn't make sense conceptually to me either.  I would think you could take the 50cal 750 amax (BC 1.050) and size it down to any caliber in the exact same shape and the BC would stay the same, but it doesn't work that way.

6, 6.5, 7, and 338 are great.  30 is good in HEAVY bullets.  25 and 27 are a little behind, but better bullets are coming out.

[Dan-o]

Shhh. 25-06= 6.5mm

Yeah, I know.

6mm Rems and 243 Win rounds look almost identical.

But then why aren't 25's popular on the long ranges?

[Dan-o]

It doesn't make sense conceptually to me either.  I would think you could take the 50cal 750 amax (BC 1.050) and size it down to any caliber in the exact same shape and the BC would stay the same, but it doesn't work that way.

6, 6.5, 7, and 338 are great.  30 is good in HEAVY bullets.  25 and 27 are a little behind, but better bullets are coming out.

 

I don't get it.....

[JimmyHoffa]

The larger bullets with same design will generally be higher BC.  The bullets increase in weight faster than surface area.  Drag force is mostly dependent on velocity squared, but also cross sectional area and shape presented.  Faster increase in weight with less increase in surface area--less effect of drag to slow the bullet, so higher BC.

[Dan-o]

That all makes sense.   Thanks.

[Bob33]

There is nothing magical about 6.5mm bullets. The issue is primarily what manufacturers offer. In 6.5mm there is a better choice of high BC bullets. Specifically, .264 bullets. A 2506 shoots .257 bullets.

[j_h_nimrod]

Shhh. 25-06= 6.5mm

Yeah, I know.

6mm Rems and 243 Win rounds look almost identical.

But then why aren't 25's popular on the long ranges?

.25-06 shoots a .257" bullet while a 6.5mm bullet is .264 and a 6mm is .243.

There is nothing more inherently accurate about bullets of .264 or .243 over the .257.  Bullets of the same shape and relative weight flying at the same muzzle velocity will increase BC as the diameter increases.  Cartridges in 25 caliber have always been a bit of a tweener round and never developed the popularity of 6 or 6.5mm, hence the reason they dominate long range.  There are many more bullet options available for the 6 n 6.5mm cartridges which gives them a practical edge. My .257 Weatherby shooting a 115 Berger Hunting VLD at ~3200fps carries almost identically to my 240 Weatherby shooting a 105 grain Berger at ~3100fps regardless that the 105 has a significantly higher BC. Given more bullet choices and wider variety of chamber inns the .257 would hold its own with any of the others.

[jasnt]

Applied Ballistics for Long Range Shooting : Understanding the elements and application of external ballistics for successful long range target shooting and Hunting

Great read and excellent info

[Dan-o]

Thanks all!

[yorketransport]

Applied Ballistics for Long Range Shooting : Understanding the elements and application of external ballistics for successful long range target shooting and Hunting

Great read and excellent info

Brian Litz is a pretty smart guy and his books do a great job of breaking down the relatively complex science of external ballistics.

Like others have said, a high BC .257 bullet is just as good as a high BC 6 or 6.5mm. The 6 and 6.5mm are popular bore diameters in target competitions so that's where the focus has been for high BC bullets. Of course if there were some premium offerings in the the .257 bore there would be more interested in it being used for long range target work. There won't be bullets until there is a demand though.

For hunting at common ranges under 400 yards, I don't think anyone would notice the difference between a 6mm, .257, or 6.5mm if they were all throwing bullets with similar BC and sectional density numbers.

Andrew

[Bofire]

  this is understandable


 http://www.exteriorballistics.com/ebexplained/5th/221.cfm
Carl

[Bofire]

and a good list

 http://www.sierrabullets.com/documents/BallisticCoefficient-rifle.pdf

Carl

[257wbymagkiller]

Bullets  now a days have come so far that you get some really high BC #s out of light bullets.  Some of the tightest groups in 1000 yard  shooting are out of .243, alot of that is BC and how "flat" it shoots.

.257 to .264 is minimal 

I don't have any 6mms but I would like to had one to the collection