Page 1 of 7 123 ... LastLast
Results 1 to 10 of 64

Thread: Question: "Muzzle Energy" vs. "Power Factor"

  1. #1
    Join Date
    Mar 2013
    Location
    California
    Posts
    72
    Feedback Score
    5 (100%)

    Question: "Muzzle Energy" vs. "Power Factor"

    All,

    I'm having trouble understanding what's more important -- "muzzle energy" (i.e. kinetic energy1) vs. "power factor" (i.e. momentum2).

    MUZZLE ENERGY

    Most of the reading I've done focuses on energy as the determining factor in the lethality of a given caliber/round. Thus, the conventional wisdom is that you need a minimum of 1,000 foot-pounds of energy to kill a deer and 3,000 foot-pounds to kill a brown bear, etc. But since energy places a lot of emphasis on speed, you can come up with some pretty ridiculous examples.

    Jellyfish: The stinger of a jellyfish is one of the fastest things in nature3. If you do the calculations, a 0.50 nanogram jellyfish stinger traveling at 45,000,000 meters/second = 0.0000000077 grains at 147,637,795.28 feet/second = 373.38 foot-pounds of energy

    Bowling Ball: At the other end of the spectrum, you have world record holders who can throw a 15 pound bowling ball at 27 miles/hour4 = 105,000 grains at 39.60 feet/second = 365.53 foot-pounds of energy

    Comparable "muzzle energy", but what would you rather have hurled at you? A microscopic needle or a 15 pound projectile? Now let's look at bullets.

    9x19mm: 115 grain Winchester FMJ bullet traveling at 1,190 feet/second5 = 361.53 foot-pounds of energy

    .45 ACP: 230 grain Winchester FMJ bullet traveling at 835 feet/second6 = 356.00 foot-pounds of energy

    Again, similar muzzle energy, but which has the better reputation for "knock down"?

    POWER FACTOR

    If we switch from energy to momentum, the numbers above change drastically:

    Jellyfish: The super fast but super light stinger has a power factor of 0.0011 kilo grain-feet/second (or 0.000023 Newton-seconds)

    Bowling Ball: The super slow but super heavy bowling ball has a power factor of 4,158 kilo grain-feet/second (or 82.12 Newton-seconds)

    Makes sense, right? A nanogram thrown at you -- even very very very fast -- ain't gonna do much to you, but a 15 pound bowling ball hurled at 27 miles/hour towards your face is going to hurt. And comparing bullets:

    9x19mm: power factor of 136.85 kilo grain-feet/second (or 2.70 Newton-seconds)

    .45 ACP: power factor of 192.05 kilo grain-feet/second (or 3.79 Newton-seconds)

    Again, makes sense: .45 is perceived as having more stopping power than 9mm.

    QUESTION

    So is muzzle energy still the king?

    If so, why is .308 Winchester (~2700 ft-lbs) considered inadequate for large predators (e.g. grizzly):
    https://www.m4carbine.net/showthread...08-for-Grizzly

    But .458 SOCOM (~2500 ft-lbs) is considered good to go?
    https://www.m4carbine.net/showthread...g-Bear-Defense

    Is it the greater power factor of .458 (600 kgr-ft/s) vs .308 (463 kgr-ft/s)? Or is it something else -- sectional density? Bullet weight and diameter? Expansion and penetration? What am I missing here?

    Taylor has one answer:
    https://en.wikipedia.org/wiki/Taylor_KO_Factor

    Looking for additional insight from the experts here at m4carbine.net

    Respectfully,
    butlers


    FOOTNOTES

    1 Source:
    https://en.wikipedia.org/wiki/Muzzle_energy

    2 Source:
    https://en.wikipedia.org/wiki/Power_...ooting_sports)

    3 Sources:
    https://www.sciencedaily.com/release...0508180735.htm
    https://www.popsci.com/jellyfish-syringe-sting

    4 Source:
    https://www.bowlingdigital.com/bowl/node/14269

    5 Source:
    https://www.luckygunner.com/winchest...fmj-ammunition

    6 Source:
    https://www.luckygunner.com/winchest...0fmjwinusa-500
    Last edited by butlers; 08-25-18 at 03:15.
    "The nation that will insist on drawing a broad line of demarcation between the fighting man and the thinking man is liable to find its fighting done by fools and its thinking done by cowards."
    William Francis Butler

  2. #2
    Join Date
    Oct 2007
    Posts
    6,762
    Feedback Score
    11 (100%)
    Simplified:

    The ability of a projectile to penetrate into and sufficiently damage the vital organs of the intended target is paramount. Expansion is a great bonus.

  3. #3
    Join Date
    Feb 2009
    Location
    Kansas
    Posts
    135
    Feedback Score
    0
    Do a search for "IWBA" (international Wound Ballistics Association), as well as Martin L. Fackler M.D. and Gary K. Roberts LCDR.

    This will get you started on the appropriate track in understanding wound ballistics.

    Your welcome....

  4. #4
    Join Date
    Jul 2006
    Location
    Oregon
    Posts
    4,629
    Feedback Score
    2 (100%)
    Neither is the short answer. It sure would be nice if some math could explain it all, nice and tidy but unfortunately it doesn't. The way the bullet acts is going to play a huge role in the wound created.

    Here is another search to try: Basic Wound Ballistic Terminal Performance Facts

  5. #5
    Join Date
    Aug 2017
    Location
    Lowcountry, SC.
    Posts
    6,142
    Feedback Score
    30 (100%)
    Its important to note that Power Factor is used to give .40 and .45 cal guns a scoring advantage in competition (USPSA) that makes up for their recoil disadvantage. Gives them an edge in scoring, in my opinion, which is why my Limited gun is a .40, and my carry guns are mostly 9mm. Has no bearing on the ability to incapacitate mammals.
    Last edited by 1168; 08-28-18 at 10:29. Reason: Spelling

  6. #6
    Join Date
    Aug 2011
    Location
    N.E. OH
    Posts
    7,591
    Feedback Score
    0
    Neither by themselves gives any indication of a bullets terminal performance.

  7. #7
    Join Date
    Sep 2007
    Posts
    3,747
    Feedback Score
    22 (100%)
    Neither mean anything in terms of a bullet's ability of incapacitate.

  8. #8
    Join Date
    May 2007
    Posts
    65
    Feedback Score
    0
    Both examples you quote are about equal. Once you get about 500 FPE with an expanding or partially fragmenting bullet things get interesting. Some people are still mystified as to why a 357 magnum is so much more effective than a 38 Special when they use the same bullet, the magnum moves about 500 fps faster which effectively doubles the energy. It is, I think the best example that explains the phenomenon in easy terms.

    Bullet construction is just as important as "energy".

    Street results for the 357 Sig are very promising, as are the results of the +P+ 9mm.

    The big problem is that too many people worry too much about their ammo and not enough about mastering their gun so that they can get consistent hits.

  9. #9
    Join Date
    Aug 2011
    Location
    N.E. OH
    Posts
    7,591
    Feedback Score
    0
    Quote Originally Posted by Nanuk View Post
    Both examples you quote are about equal. Once you get about 500 FPE with an expanding or partially fragmenting bullet things get interesting. Some people are still mystified as to why a 357 magnum is so much more effective than a 38 Special when they use the same bullet, the magnum moves about 500 fps faster which effectively doubles the energy. It is, I think the best example that explains the phenomenon in easy terms.

    Bullet construction is just as important as "energy".

    Street results for the 357 Sig are very promising, as are the results of the +P+ 9mm.

    The big problem is that too many people worry too much about their ammo and not enough about mastering their gun so that they can get consistent hits.

    Can you share what +p+ 9mm loads have good street results?

  10. #10
    Join Date
    Feb 2012
    Posts
    106
    Feedback Score
    0
    Quote Originally Posted by MegademiC View Post
    Can you share what +p+ 9mm loads have good street results?
    Winchester Ranger 127-grain +P+.

    Orlando PD has been using it for years.

Page 1 of 7 123 ... LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •