Long Range Hunting Online Magazine Hypothetical BC question
 Home LRH Store Forums Long Range Rifles Articles Reviews Group Hunts Shooting Classes G7 Ballistics Calculator Rules & FAQ Register Search Today's Posts Mark Forums Read

 Rifles, Bullets, Barrels & Ballistics

# Hypothetical BC question

#1
03-06-2011, 03:56 PM
 Gold Member Join Date: Oct 2008 Location: Wherever the Marine Corps sends us. Posts: 676
Hypothetical BC question

Assuming two bullets have the same exterior measurements, are of the ULD type design with RBBT, and both balance well. If one bullet weighs say 215 gr and the other weighs 240 gr, which would have the higher BC? Let's say these are .30 cal bullets traveling 3200 fps for the 215 and 3150 for the 240. I'm not trying to start an argument, just curious as to everyone's opinions.

Thanks
__________________
ACTIVE DUTY MARINE CORPS '96-'04
SERGEANT (MED RET)
COMBAT ENGINEER, MOUT INSTRUCTOR, RIFLE/PISTOL INSTRUCTOR

"Be polite, be professional, but have a plan to kill everyone you meet."
"I come in peace. I didn't bring artillery. But I'm pleading with you, tears in my eyes: If you f*ck with me, I'll kill you all." Marine General Mattis

Custom built 7mm SAUM
#2
03-06-2011, 05:24 PM
 Silver Member Join Date: Sep 2008 Posts: 327
Re: Hypothetical BC question

wikipedia - ... "BC is a function of mass, diameter, and drag coefficient." It is given by the mass of the object divided by the diameter squared that it presents to the airflow divided by a dimensionless constant i that relates to the aerodynamics of its shape. Ballistic coefficient has units of lb/inē or kg/mē. BCs for bullets are normally stated in lb/inē by their manufacturers without referring to this unit..."

or in other words,

BC = sectional density/form factor
__________________
#3
03-06-2011, 05:27 PM
 Platinum Member Join Date: Feb 2004 Location: Pennsyltucky Posts: 2,630
Re: Hypothetical BC question

the heavier bullet will have a higher BC.
#4
03-06-2011, 05:29 PM
 Official LRH Sponsor Join Date: Mar 2007 Posts: 634
Re: Hypothetical BC question

To put the above information into the context of your specific question...

If they're truly the same shape,
the 240 grain bullet will have a BC that's 1.116 times higher than the 215 at all speeds.

Because 240/215 = 1.116.

That's 11.6% higher BC for the 240 grain.

So if the 215 has a BC of .665 at a given speed (or averaged over a given speed range), then the 240 will have a BC of .665*1.116 = .742.

Bear in mind the 240 will suffer depressed MV, so the performance of the heavier bullet won't be as much better as the BC implies, but it will be a little better even at a reduced MV assuming equal chamber pressure for both bullets.

-Bryan
#5
03-07-2011, 12:18 AM
 Platinum Member Join Date: May 2008 Location: South of Canada and North of Wyoming Posts: 6,068
Re: Hypothetical BC question

Quote:
Quote:
 Originally Posted by JARHEAD1371 Assuming two bullets have the same exterior measurements, are of the ULD type design with RBBT, and both balance well. If one bullet weighs say 215 gr and the other weighs 240 gr, which would have the higher BC? Let's say these are .30 cal bullets traveling 3200 fps for the 215 and 3150 for the 240. I'm not trying to start an argument, just curious as to everyone's opinions. Thanks
Well it all depends.....
#6
03-07-2011, 03:07 AM
 Gold Member Join Date: Oct 2008 Location: Wherever the Marine Corps sends us. Posts: 676
Re: Hypothetical BC question

Quote:
 Originally Posted by bsl135 To put the above information into the context of your specific question... If they're truly the same shape, the 240 grain bullet will have a BC that's 1.116 times higher than the 215 at all speeds. Because 240/215 = 1.116. That's 11.6% higher BC for the 240 grain. So if the 215 has a BC of .665 at a given speed (or averaged over a given speed range), then the 240 will have a BC of .665*1.116 = .742. Bear in mind the 240 will suffer depressed MV, so the performance of the heavier bullet won't be as much better as the BC implies, but it will be a little better even at a reduced MV assuming equal chamber pressure for both bullets. -Bryan
Thanks for breaking it down for me. It makes more sense now.
__________________
ACTIVE DUTY MARINE CORPS '96-'04
SERGEANT (MED RET)
COMBAT ENGINEER, MOUT INSTRUCTOR, RIFLE/PISTOL INSTRUCTOR

"Be polite, be professional, but have a plan to kill everyone you meet."
"I come in peace. I didn't bring artillery. But I'm pleading with you, tears in my eyes: If you f*ck with me, I'll kill you all." Marine General Mattis

Custom built 7mm SAUM
#7
03-07-2011, 10:47 AM
 Platinum Member Join Date: Apr 2010 Location: Allen, TX Posts: 2,608
Re: Hypothetical BC question

Also, they won't be exactly the same shape if they are made from the same material/construction. The heavier bullet will be longer.

 Bookmarks

 Thread Tools Display Modes Linear Mode

 Similar Threads for: Hypothetical BC question Thread Thread Starter Forum Replies Last Post hjl General Discussion 28 02-25-2009 12:31 AM superlite17 Long Range Scopes and Other Optics 6 06-05-2007 08:48 AM larryaguilar Rifles, Bullets, Barrels & Ballistics 7 03-01-2003 12:10 AM

All times are GMT -5. The time now is 11:11 PM.