Comparing performance

ncrypt · November 25, 2015, 06:49 PM

This may be a stupid question, but in general discussions with my buddies about performance from different rifle calibers, I always reference my reloading manuals to review velocities and bullet weights.

Is velocity the primary factor that determines the kinetic energy at a given distance?

cjwils · November 25, 2015, 07:04 PM

Kinetic energy equals 1/2 times mass times the square of velocity. That squaring makes velocity the major factor.

Brian Pfleuger · November 25, 2015, 07:37 PM

Velocity is the only thing that changes with distance and therefore it is the variable that determines the changing kinetic energy over distance.

The technical formua is KE = 1/2•m•v^2 but for us hunters the easy way is projectile mass in grains times feet per second divided by 450,240.

However, there's a lot more to "comparing performance" than kinetic energy.

jmr40 · November 26, 2015, 09:20 AM

This is a complex issue with no easy answer. What matters is bullet penetration, and expansion. Figuring energy doesn't take into account bullet construction. Many modern bullets have made for some pretty effective kills using smaller bullets with far less energy than normally considered possible. A 130 gr copper bullet fired from a 308 @ 3000 fps will out penetrate a 180 gr lead bullet fired from a 300 magnum @ 3000 fps.

While not perfect, the best method I've found to predict performance is to find the minimum speed a particular bullet needs at impact to expand properly. That is the maximum effective range for that gun.

Remember it is the speed at impact that matters, not at the muzzle, and aerodynamic bullets make a huge difference even at moderate ranges. I can take a very aerodynamic bullet, load it in a 308 at only 2500 fps and at 200 yards it is moving faster, with more energy than a round nose bullet fired from a 300 WM at 3000 fps.

A 308 using modern bullets CAN be more effective than a 300 WM loaded with old school bullets. But you can always use the better bullets in the 300 WM and beat 308.

g.willikers · November 26, 2015, 10:22 AM

The more complicated the evidence, the better chance of confusing your buddies to a stand still.
Always useful in winning arguments.

ncrypt · November 26, 2015, 11:04 AM

thanks guys. Great info

November 25, 2015, 06:49 PM	#1
ncrypt Member Join Date: December 3, 2013 Posts: 72	Comparing performance This may be a stupid question, but in general discussions with my buddies about performance from different rifle calibers, I always reference my reloading manuals to review velocities and bullet weights. Is velocity the primary factor that determines the kinetic energy at a given distance?

November 25, 2015, 07:37 PM	#3
Brian Pfleuger Moderator Emeritus Join Date: June 25, 2008 Location: Austin, CO Posts: 19,578	Velocity is the only thing that changes with distance and therefore it is the variable that determines the changing kinetic energy over distance. The technical formua is KE = 1/2•m•v^2 but for us hunters the easy way is projectile mass in grains times feet per second divided by 450,240. However, there's a lot more to "comparing performance" than kinetic energy. __________________ Nobody plans to screw up their lives... ...they just don't plan not to. -Andy Stanley

November 26, 2015, 10:22 AM	#5
g.willikers Senior Member Join Date: September 28, 2008 Posts: 10,442	The more complicated the evidence, the better chance of confusing your buddies to a stand still. Always useful in winning arguments. __________________ Walt Kelly, alias Pogo, sez: “Don't take life so serious, son, it ain't nohow permanent.”

November 25, 2015, 07:04 PM	#2
cjwils Senior Member Join Date: November 28, 2010 Location: Washington state Posts: 401	Kinetic energy equals 1/2 times mass times the square of velocity. That squaring makes velocity the major factor.

November 26, 2015, 09:20 AM	#4
jmr40 Senior Member Join Date: June 15, 2008 Location: Georgia Posts: 10,808	This is a complex issue with no easy answer. What matters is bullet penetration, and expansion. Figuring energy doesn't take into account bullet construction. Many modern bullets have made for some pretty effective kills using smaller bullets with far less energy than normally considered possible. A 130 gr copper bullet fired from a 308 @ 3000 fps will out penetrate a 180 gr lead bullet fired from a 300 magnum @ 3000 fps. While not perfect, the best method I've found to predict performance is to find the minimum speed a particular bullet needs at impact to expand properly. That is the maximum effective range for that gun. Remember it is the speed at impact that matters, not at the muzzle, and aerodynamic bullets make a huge difference even at moderate ranges. I can take a very aerodynamic bullet, load it in a 308 at only 2500 fps and at 200 yards it is moving faster, with more energy than a round nose bullet fired from a 300 WM at 3000 fps. A 308 using modern bullets CAN be more effective than a 300 WM loaded with old school bullets. But you can always use the better bullets in the 300 WM and beat 308.

November 26, 2015, 11:04 AM	#6
ncrypt Member Join Date: December 3, 2013 Posts: 72	thanks guys. Great info