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# Rifle Cartridge Efficiency Formula

#1
08-11-2014, 09:04 PM
 Silver Member Join Date: May 2014 Location: North East Missouri Posts: 103
Rifle Cartridge Efficiency Formula

I was just wondering if there's a formula for rifle cartridge efficiency taking the Ballistic Coefficient of the Bullet, the Sectional Density of the Bullet, the Bullet Weight, the Velocity of the Bullet, the Taylor Index of the Bullet, the Powder Charge of the Cartridge, and the Recoil of the Cartridge ? If there is a formula please let me know if not could someone please make one or explain why or why not one of the parameters could or couldn't be used. Thanks
#2
08-12-2014, 08:10 AM
 Gold Member Join Date: Feb 2008 Posts: 741
Re: Rifle Cartridge Efficiency Formula

Quote:
 Originally Posted by 375rifleman I was just wondering if there's a formula for rifle cartridge efficiency taking the Ballistic Coefficient of the Bullet, the Sectional Density of the Bullet, the Bullet Weight, the Velocity of the Bullet, the Taylor Index of the Bullet, the Powder Charge of the Cartridge, and the Recoil of the Cartridge ? If there is a formula please let me know if not could someone please make one or explain why or why not one of the parameters could or couldn't be used. Thanks
The reason why not is far simpler than the reason you can take all of those parameters into consideration for one formula.
One, BC is an external ballistics parameter, two, SD is a terminal ballistics parameter which doesn't use the BC of a bullet, or in other words, it's construction and shape or it's velocity to come to a figure of any significance, 3, velocity alone means little, 4 weight alone also means little, 5, the powder charge means little, 6, the recoil is just a fact of life and 7, Taylors Knockout index is also flawed because it bases it's figures on weight and bullet diameter to knockout an elephant from any angle, there are many cartridges that will kill far better than what the Taylor index would suggest.

I really don't know what you are looking to discover, but there are already in place many DIFFERENT formula's out there that calculate myriad aspects of ballistics, of which there are 3 distinct different aspects of ballistics, 1, internal ballistics, from cartridge ignition to bullet exit, 2 external ballistics, bullet flight, and 3, terminal ballistics, from bullet impact in a medium to bullet stop and what that bullet does.

Hope this answers some questions for you, if not, good luck finding an answer, if you do find a formula, please let us know. I would be interested in reading it.

Cheers.
#3
08-12-2014, 07:35 PM
 Platinum Member Join Date: Aug 2003 Location: NC, oceanfront Posts: 3,690
Re: Rifle Cartridge Efficiency Formula

It's probably possible to define a combination that is neutral across the board.
That is, best at nothing AND worst at nothing.

In other words -factory rifle/factory chamber.
#4
08-12-2014, 09:25 PM
 Gold Member Join Date: Sep 2006 Location: The Motherlode Posts: 655
Re: Rifle Cartridge Efficiency Formula

It would be easier to first define what you want to do. Elk at 1000 or prairie dogs at 400? Then narrow it down to some cartridges you're interested in without pushing the limits. Get a load manual or look at Nosler or Hodgdon online data and figure out how fast your cartridges can reasonably be expected to launch a high weigh/BC for caliber bullet and see how it compares to your goal.

Either that or just go buy a 7mm Rem Mag for the stuff bigger than a coyote and a .243 for everything smaller and be happy the rest of your life.
__________________
Now it's time fore me to go. The Autumn moon lights my way.
#5
08-12-2014, 11:09 PM
 Silver Member Join Date: Apr 2010 Location: ND Posts: 352
Re: Rifle Cartridge Efficiency Formula

What is the least amount of energy required to make x amount of energy at x distance. That would be efficiency. A loaded cartridge has potential energy and a bullet in flight has kinetic energy. PE is determined by the charge weight, specific heat of the powder, and bullet mass. When fired the pe loses most of the energy through heat and recoil, with the balance sending the bullet off. That's when BC comes into play. Norma's new manual talks about it a little bit. Someone here smarter than me could derive a formula that would solve this...
#6
08-13-2014, 06:07 AM
 Gold Member Join Date: Sep 2006 Location: The Motherlode Posts: 655
Re: Rifle Cartridge Efficiency Formula

There isn't anything to solve. It's like trying to draw a smiley face on a spinning tire. You'll just keep going round and round in circles. Personally I looked at overbore (whatever that is) charts and decided to ditch my .270 and go to a 7mag. If my brother didn't already shoot one I would have stayed with the .270. With the new high BC .277 bullets I would have been very happy too.

There's a reason the .270, .30-06, 7mm Rem Mag and .300 Win Mag have been so popular for so long. They are efficient enough to launch bullets heavy enough to kill at substantial ranges any North American big game without destroying your shoulder or being hard to load for. In the end it all comes down to what your chosen bullet, load, rifle and most importantly YOU the shooter are capable of. Knowing and sticking to those limitations is up to you.
__________________
Now it's time fore me to go. The Autumn moon lights my way.
#7
08-13-2014, 07:21 AM
 Silver Member Join Date: Sep 2012 Location: Michigan Posts: 161
Re: Rifle Cartridge Efficiency Formula

Quote:
 Originally Posted by MagnumManiac SD is a terminal ballistics parameter which doesn't use the BC of a bullet, or in other words, it's construction and shape or it's velocity to come to a figure of any significance,
SD and BC are directly related and are important to external ballistics solutions. Ballistic Coefficient is a function of Sectional Density and Form Factor.

A cartridge's efficiency is a matter of Internal Ballistics.

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