Differences in posted BC's ?

[Old Corps 8541]

Doing a bit of "window shopping" for 30 Cal. bullets and found some questionable info ;
On MidSouth the following 168/169 BC's are listed;
Speer 168 BTHP .534
Nosler 168 BTHP .462
Hornady 168 BTHP .450
Sierra 169 BTHP .527
hornady ELD M .523
Sierra TKM .535
I know BC dosen't mean much IF the bullet can't be made to shoot small groups at a mid range distance, but it seams to me like some "fuzzy math" is being used to come up with these BC's ?

 

[ma smith]

Marketing 101: use the biggest numbers allowed by law.
BCs at high velocity and low distance from muzzle= higher.

eg: https://www.hornady.com/support/ballistic-coefficient

Hornady originally published “800 yard”* average Ballistic Coefficient (BC) values for ELD-X and ELD Match bullets. This was done to provide the most usable BC from a trajectory prediction standpoint. Unfortunately, many shooters did not understand that Hornady was listing a more useable “800 yard” BC while other manufacturers list “200 yard”* BCs. When doing pre-purchase research either on the web or at the store, the increased performance of the ELD Match and ELD-X bullets wasn’t always realized in a head-to-head BC comparison.

For long range shooting, you really do need BCs valid at (eg) 800yd+
These BCs are smaller, but people don't like smaller numbers.
As a result, OEMs now all publish the bigger numbers.

 

[OREGUN]

Doing a bit of "window shopping" for 30 Cal. bullets and found some questionable info ;
On MidSouth the following 168/169 BC's are listed;
Speer 168 BTHP .534
Nosler 168 BTHP .462
Hornady 168 BTHP .450
Sierra 169 BTHP .527
hornady ELD M .523
Sierra TKM .535
I know BC dosen't mean much IF the bullet can't be made to shoot small groups at a mid range distance, but it seams to me like some "fuzzy math" is being used to come up with these BC's ?

What seems fuzzy?

 

[rustyinbend]

Over my years in reloading ... I've found Berger BC's to most accurately reflect reality ... but that's just me. The only way to know for sure, is to get a vertical impact reading at 1000 yards, and then true the BC to velocity and drop. I never trust the box numbers for competition loads.

 

[Taylorbok]

I have ever only used Bergers, SIerra and Hornady but I've always had posted BC close enough to hit an IPSIC at 1000

 

[Sig Marine]

BC’s change with form factor; even though the bullets are of the same weight, they are NOT the same shape. This changes how drag can affect their flight

 

[OREGUN]

BC’s change with form factor; even though the bullets are of the same weight, they are NOT the same shape. This changes how drag can affect their flight

I think this, more than anything, accounts for the differences you’re seeing. Maybe some data collection methodology differences too. Get one of these bullets (any) going close to the top of its reasonable speed range and the bc on the box will be pretty close.

 

[FredHammer]

I look them up in Litz book. Look at the velocity band I'm firing and use that corrected BC. Pretty close!

Hornady listed BC are very close
Berger, hate to say are .055 or more

 

[Doom]

To the point on shape:

Speer 168 BTHP .534 This one is strange Tangent Ogive
Nosler 168 BTHP .462 Tangent Ogive
Hornady 168 BTHP .450 Tangent Ogive
Sierra 169 BTHP .527 Hybrid (combination tangent/secant)
hornady ELD M .523 Hybrid
Sierra TKM .535 Secant Ogive

The boat tail design also affect the BC. There is also no standard test for the BC and since the G1 ballistic coefficient isn't for boatail bullsts the BC series with Mach Number (velocity). Only Sierra has taken this into account for there bullets.