close
Long Range Hunting Online Magazine


Go Back   Long Range Hunting Online Magazine > Rifles, Reloading, Optics, Equipment > Rifles, Bullets, Barrels & Ballistics

Rifles, Bullets, Barrels & Ballistics Applied Ballistics

Reply

Hypothetical BC question

LinkBack Thread Tools Display Modes
  #1  
Unread 03-06-2011, 03:56 PM
Gold Member
 
Join Date: Oct 2008
Location: Wherever the Marine Corps sends us.
Posts: 674
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
Reply With Quote
  •   #2  
    Unread 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
    __________________
    Reply With Quote

      #3  
    Unread 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.
    Reply With Quote
      #4  
    Unread 03-06-2011, 05:29 PM
    Official LRH Sponsor
     
    Join Date: Mar 2007
    Posts: 633
    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
    Reply With Quote
      #5  
    Unread 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 View Post
    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.....
    Reply With Quote
      #6  
    Unread 03-07-2011, 03:07 AM
    Gold Member
     
    Join Date: Oct 2008
    Location: Wherever the Marine Corps sends us.
    Posts: 674
    Re: Hypothetical BC question

    Quote:
    Originally Posted by bsl135 View Post
    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
    Reply With Quote
      #7  
    Unread 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.
    Reply With Quote
    Reply

    Bookmarks

    Thread Tools
    Display Modes


    Similar Threads for: Hypothetical BC question
    Thread Thread Starter Forum Replies Last Post
    hypothetical which state to live in the USA hjl General Discussion 28 02-25-2009 12:31 AM
    DUMB Question... really dumb magnificcation question.. but PLEASE HELP superlite17 Long Range Scopes and Other Optics 6 06-05-2007 08:48 AM
    bedding question/Primer Question larryaguilar Rifles, Bullets, Barrels & Ballistics 7 03-01-2003 12:10 AM


    All times are GMT -5. The time now is 04:25 AM.


    Powered by vBulletin ©2000 - 2017, Jelsoft Enterprises Ltd.
    Content Management Powered by vBadvanced CMPS
    All content ©2010-2015 Long Range Hunting, LLC