Nerd alert. Same bullet at different speed, BC assumptions?

[SDHNTR]

Assume same bullet from a .300wm going 3000 fps and and going from a .308 at 2650. What’s the effective change in BC when the same bullet is used in different cartridges/at different speeds?


Or say, a 6.5 prc going 3100 vs a Creedmore going 2850.


Stated another way…. A bullet manufacturer posts a BC figure based on a certain velocity. If I’m shooting that same bullet out of a different cartridge at a significantly different speed, how can I assume the bc to change? Higher or lower BC with more or leas speed?

 

[z987k]

I think only Sierra publishes BC ranges for different speeds. Every one has a higher BC at the higher velocity. Off the top of my head, I'm guessing this has to do with the difference in Reynolds numbers at the different speeds.

 

[JFK]

I don’t know the answer to your question, but I believe this is what custom drag curves take into account. Using BC’s is an approximation of what is actually happening and they are pretty accurate, but in reality the bc is degrading from muzzle to target.

 

[Formidilosus]

Assume same bullet from a .300wm going 3000 fps and and going from a .308 at 2650. What’s the effective change in BC when the same bullet is used in different cartridges/at different speeds?


Or say, a 6.5 prc going 3100 vs a Creedmore going 2850.


Stated another way…. A bullet manufacturer posts a BC figure based on a certain velocity. If I’m shooting that same bullet out of a different cartridge at a significantly different speed, how can I assume the bc to change? Higher or lower BC with more or leas speed?

Around 10 points or so. It’s not enough to matter inside the terminal range bullets, and nearly zero people could actually see and measure the difference on target.

 

[SDHNTR]

10 points as in .010? Wouldn’t it be more of a percentage difference? And is there a positive or negative correlation with speed?

 

[Lawnboi]

This is why CDM and 4k of profiles exist. But really for what hunters are looking at ~2k fps impact, they really are overkill.

Hornady, and sierra list Mach data.

Ballistic Coefficient - Hornady Manufacturing, Inc

A-Tip®, ELD® Match, and ELD-X® Ballistic Coefficient Values 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 st...

www.hornady.com

 

[SDHNTR]

This is why CDM and 4k of profiles exist. But really for what hunters are looking at ~2k fps impact, they really are overkill.

Hornady, and sierra list Mach data.

Ballistic Coefficient - Hornady Manufacturing, Inc

A-Tip®, ELD® Match, and ELD-X® Ballistic Coefficient Values 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 st...

www.hornady.com

Great article. Thanks. That’s the best explanation I’ve found.