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

JBM ballistics calculator question

LinkBack Thread Tools Display Modes
  #1  
Unread 02-16-2011, 07:58 PM
Gold Member
 
Join Date: Jan 2010
Location: NC mountains
Posts: 508
JBM ballistics calculator question

I have a 20MOA base on my rig. Does one enter this information in JBM? I see an input for cant angle, but it's in degrees.
Reply With Quote
  •   #2  
    Unread 02-16-2011, 08:10 PM
    KRP KRP is offline
    Gold Member
     
    Join Date: Dec 2007
    Location: Kuna, ID
    Posts: 594
    Re: JBM ballistics calculator question

    Doesn't matter, cant angle in JBM is something else.
    Reply With Quote

      #3  
    Unread 02-16-2011, 08:16 PM
    Gold Member
     
    Join Date: Jan 2010
    Location: NC mountains
    Posts: 508
    Re: JBM ballistics calculator question

    Quote:
    Originally Posted by KRP View Post
    Doesn't matter, cant angle in JBM is something else.
    Ok, thanks for the reply. I figured if it mattered they would have had an input for it.
    Reply With Quote
      #4  
    Unread 02-16-2011, 08:47 PM
    Silver Member
     
    Join Date: Oct 2008
    Location: Bryan, Tx
    Posts: 284
    Re: JBM ballistics calculator question

    No it doesn't matter for a 20MOA rail. What does matter is your zero point. This compensates for the 20 MOA rail. Don't forget an accurate scope height too!
    Reply With Quote
      #5  
    Unread 02-16-2011, 09:05 PM
    Gold Member
     
    Join Date: Jan 2010
    Location: NC mountains
    Posts: 508
    Re: JBM ballistics calculator question

    Quote:
    Originally Posted by nheninge View Post
    No it doesn't matter for a 20MOA rail. What does matter is your zero point. This compensates for the 20 MOA rail. Don't forget an accurate scope height too!
    I have 1.125" rings. That will be the number that I input right?
    Reply With Quote
      #6  
    Unread 02-16-2011, 09:20 PM
    Silver Member
     
    Join Date: Oct 2008
    Location: Bryan, Tx
    Posts: 284
    Re: JBM ballistics calculator question

    No. Roughly put, you need the distance from the center of your scope to the center of your chamber. Several formulas are available in different threads. You can estimate with a micrometer, or calculate the actual measurements and plug in to formula (i.e. 1/2 scope diameter plus 1/2 chamber diameter plus distance between bottom of scope and top of chamber). This is the actual starting point of the bullet so this height is pretty important.
    Reply With Quote
      #7  
    Unread 02-16-2011, 09:29 PM
    Bronze Member
     
    Join Date: Dec 2009
    Location: middle tn
    Posts: 72
    Re: JBM ballistics calculator question

    Measure the dia of the barrel below the bell, divide by 2.
    Measure the dia of the bell, divide by 2.
    Measure the distance from the top of the bell to the top of the barrel and subtract half the dia of the bell from that dim and add half the the dia of the barrel.

    That will give you the distance from the center line of the scope to the center line of the bore. Enter that number in your JBM calculator.
    __________________
    don't ever be fooled into believing security is a good alternative for freedom.
    Reply With Quote
    Reply

    Bookmarks

    Thread Tools
    Display Modes


    Similar Threads for: JBM ballistics calculator question
    Thread Thread Starter Forum Replies Last Post
    ballistics calculator hank1919 Website & Forum Support 3 08-26-2011 10:24 PM
    ballistics calculator NVRILEY Rifles, Bullets, Barrels & Ballistics 2 01-23-2011 12:29 AM
    Ballistics Calculator For Blackberry jcknight007 General Discussion 0 06-02-2010 11:32 AM
    Warm up your Ballistics Calculator! bigngreen Rifles, Bullets, Barrels & Ballistics 14 03-05-2010 11:30 PM
    Ballistics Calculator Problems! lomfs24 Rifles, Bullets, Barrels & Ballistics 14 02-17-2010 11:05 PM


    All times are GMT -5. The time now is 01:52 PM.


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