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Thread: muzzle energy

  1. #1

    Default muzzle energy

    Can anyone tell me how to figure muzzle energy? I have a hand gun shooting 120 gr. bullets at 2075 fps. I read somewhere that you need about 1000 ft. lbs. of energy for deer sized game. Will this load be sutiable for deer sized game out to 150 yds? The gun is a T.C. Contender 10" barrell in 7-30 Waters. Thanks for any help you can give me.

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    See .jpg that is attached.
    I added a excel workbook if that helps.
    1147 ft-lbs.
    Last edited by travelers; 03-19-2010 at 07:39.
    "The older I get, the better I was."

  3. #3

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    KE= 1/2 M (v2) or Kinetic Energy = 1/2 Mass times velocity squared.

    You can calculate it easy with a number of online ballistic calcs like this one...

    http://www.biggameinfo.com/BalCalc.aspx

    Having said that, I dont put much stock in KE numbers. You need to know what velocity your hunting bullets expand at, what their terminal characteristics are like and if they have enough momentum to penetrate and cause fatal damage. I think a lot of handgun cartridge/load combos with less than 1000 ftlb are more than adequate to get the job done. On the flip side, a 250 gr Accubond going less than 1800 fps (minimum opening velocity for the AB) will pencil through, causing little damamge and high likelyhood of a runaway deer. Another reason I think the 1000 ftlb KE number is bogus for deer is that there are a lot of sizes of deer ranging from less than a 100 lbs to over 400 lbs. Bottom line, will your handgun and bullet perform? If you can penetrate 2 milk jugs of water back to back (about 12") you can kill a deer with a good shot to the boiler room.

    Cheers,

    Mark

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    MontanaRifleman, nice link.
    Ran some numbers for my 45/70, got enough ummpphh to kill a 173# doe at 500yds.
    Only has 224.5" of drop.

    Might have to pound a falling wedge under the front scope mount.

    ,
    "The older I get, the better I was."

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    Energy (foot-lbs) = Bullet Weight in Grains * Velocity (fps) ^2 /450800.

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    You'll probably want that wedge under the REAR scope mount, it'll work better that way.

  7. #7

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    Quote Originally Posted by bandhmo View Post
    Energy (foot-lbs) = Bullet Weight in Grains * Velocity (fps) ^2 /450800.
    Bandhmo, that would be the formula for momentum (P=mv), which is more representative of a bullets actual penetrating force than KE which only uses half the mass and squares the velocity, which is not a ballanced look at the bullets actual potential. The correct formula for energy is in my earlier post.

    KE is measured in ft lbs and momentum in lb ft/sec.

    Mark

  8. #8

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    When you start talking energy at distance, you need to figure in the ballistic coefficient of the bullet along with the MV. I just use the ballistics tables in the back of the reloading manuals. I just happened to grab the Hornady manual (though in my experience the Sierra Single Shot Pistol bullet is much better for your needs.) At the muzzle their 120 grain HP started at 2100fps has a ME of 1175 fp. At 100 yards its doing 1872fps for 933fp and at 200 it's doing 1661fps for 735 fp.

    Now on to the bigger question, that 1000 foot pounds. Nah.

    It's an arbitrary number, and with a good expanding bullet like the Sierra I'd have complete faith in your round to past 200 for deer with a lung hit. In fact I've taken a couple of deer at between 225 and 250 with the Sierra out of a 7mm TCU Contender. I've had notable failures to expand anywhere past 100 yard with most other 7mm bullets in the velocity range you're talking. They're just too stoutly built for the job.

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    Quote Originally Posted by gunbugs View Post
    You'll probably want that wedge under the REAR scope mount, it'll work better that way.
    Now I know way I can't hit nothin.....

    banbhmo posted the same formula as I did, I got the formula out of the Lyman reloading
    manual.
    I googled and found reference to both bandhmo and montanarifleman formula.

    So which one is correct?????
    I don't know, that's why I'm asking.
    "The older I get, the better I was."

  10. #10

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    Quote Originally Posted by travelers View Post
    So which one is correct?????
    I don't know, that's why I'm asking.
    They are both correct and I posted both.

    There are two measurments of "power" commonly used when talking about external ballistics. The most commom/popular of these two is KE (energy). The other is momentum.

    Momentum is the best measurment of a bullets force or power, and potential to penetrate. It is simply the product of multiplying the mass against the velocity.

    P (momentum) = m (mass) times v (velocity)

    KE is basically a hype figure used by manufactures to sell rifles and ammo and has very little to do with anything prcticle about shooting or killing. The formula IS...

    KE= 1/2m times v squared.

    This formula (energy) produces big numbers which sound impressive.

    If we take a 240 gr bullet at 2000 fps it will produce a KE of 2142 lb ft., and a Momentum of 68 ft lbs/sec. Which sounds more impressive?

    Now if we take a 120 gr bullet at 4000 fps the energy jumps way up to 4263 ft lbs, but the momentum remains the same. The momentum is the "better" reflection of the bullets real force. A bullet half the size going at twice the speed does not have twice the force of the heavier, slower bullet.

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    Quote:
    Quote:
    Originally Posted by bandhmo
    Energy (foot-lbs) = Bullet Weight in Grains * Velocity (fps) ^2 /450800.


    Bandhmo, that would be the formula for momentum (P=mv), which is more representative of a bullets actual penetrating force than KE which only uses half the mass and squares the velocity, which is not a ballanced look at the bullets actual potential. The correct formula for energy is in my earlier post.

    KE is measured in ft lbs and momentum in lb ft/sec.

    Mark
    That formula is for Energy. I could not figure out how to make the 2 a super script so I used the "^2" to show squared.

    The whole energy vs. momentum debate has gone on for over 100 years and will go on many more. Both numbers have a place. Personally I think both are about meaningless, other then as a very general guide to what a gun can do.

  12. #12

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    Should of added this to first post. The bullet I am shooting is a 120 gr. Sierra. Where I am hunting with this round I will have a maxium shot of 150 yards. Most shots will be less than 100 yards at 175 lb. max whitetail. I am shooting 37.0 grains of Win. 748. Gun will group at 1.5 inches at 100 yards or better. Is this a good setup or does someone know something better for this gun?

  13. #13

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    The gun sounds great. If you do your part, it should do it's job nicely.

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    Quote Originally Posted by Cast Iron View Post
    Should of added this to first post. The bullet I am shooting is a 120 gr. Sierra. Where I am hunting with this round I will have a maxium shot of 150 yards. Most shots will be less than 100 yards at 175 lb. max whitetail. I am shooting 37.0 grains of Win. 748. Gun will group at 1.5 inches at 100 yards or better. Is this a good setup or does someone know something better for this gun?
    Put the Sierra in the right place and you'll have no problems.

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    MontanaRifleman - Thanks for the link! With my 500 Gr. handloads for my .450 Marlin, my "optimal game weight" doesn't fall below a ton until 100 yards. Perfect brown bear medicine.

    The other 299,300,000 people can have it.

    Noone has a more intimate understanding of, or deeper appreciation for freedom, than a soldier who has fought for it in a country where it does not exist.

  16. #16

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    Quote Originally Posted by AKsoldier View Post
    MontanaRifleman - Thanks for the link! With my 500 Gr. handloads for my .450 Marlin, my "optimal game weight" doesn't fall below a ton until 100 yards. Perfect brown bear medicine.
    You're welcome, but I dont look at the game weight column If you calculate the defaults on that page, it says a 180 gr 30 cla bullet with an MV of 3000 fps is only good on game up to 380 lbs at 500 yds, which rules out a bull elk that is over twice that. That bullet @ 500 yds is traveling 1980 fps with a KE of 1576 and momentum of 51 lbft which is very adequate for a bull elk. Bottom line is will the bullet (with a given mass and particular type of construction) penetrate and give good terminal performance at a given velocity. I think your 500 gr pill will rpobably do the job. What type of bullet is it and what's the MV?

  17. #17

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    Quote Originally Posted by MontanaRifleman View Post
    They are both correct and I posted both.

    There are two measurments of "power" commonly used when talking about external ballistics. The most commom/popular of these two is KE (energy). The other is momentum.
    From a pure physics perspective you have misused the term "power."

    Power = work/time and work = force x distance and force = mass x acceleration.

    Power, Kinetic energy and Momentum are different measurments. Watts, foot/lbs, and Ns.

    Power, Kinetic energy and momentum are not interchangeable terms.

  18. #18

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    Quote Originally Posted by seant View Post
    From a pure physics perspective you have misused the term "power."

    Power = work/time and work = force x distance and force = mass x acceleration.

    Power, Kinetic energy and Momentum are different measurments. Watts, foot/lbs, and Ns.

    Power, Kinetic energy and momentum are not interchangeable terms.
    You are quite correct, I was using the term power in a genarl sense in order to convey an idea. That's why I "quoted" it.

    Thanks for keeping things straight

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    Default Ouch!

    My head hurts.

    I killed more animals with more guns when I was a youngster who didn't know about all this technical mumbo-jumbo. I never considered my 250 Savage under powered for the whitetail it took at 302 yds, nor my 30-30 as difficult to shoot at 178 yds because the bullet drop from my 80 yd zero was so great. I just took the time to make the shot, put the bullet where it needed to go and got to work with the gutting knives and drag sled. I've seen multiple deer drop dead-on-the-spot from a little 25-20 (Dad's cousin...excellent shot and the quietest man I've ever seen move through the woods), and I've tracked one hit with a 257 Wby for a little over 800 yds before it died (Dad's Uncle...lived in ballistic charts and thought speed compensated for poor stalking and accuracy).

    Bottom line: A well constructed bullet from basically ANY centerfire rifle cartridge properly delivered is plenty to kill whitetail deer at commonly (MR, that's for you ) encountered hunting ranges. The biggest variable and stumbling block is the skill of the marksman and their knowledge and ability to put the bullet where it needs to go.

    As to the OP's question: The 7-30 Waters is plenty of gun for a whitetail deer. Put the bullet in the heart/lung area and the deer will die quickly and ethically, regardless how much kinetic energy, momentum, power, or other mathematic figure the bullet may have when it impacts. Good luck and happy hunting.

  20. #20

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    Quote Originally Posted by Diesel Nut View Post
    The biggest variable and stumbling block is the skill of the marksman and their knowledge and ability to put the bullet where it needs to go.
    That's it, front back and middle. Guys try to buy or read their way into success. But it's feet on the ground and skill that make all the difference. Can't buy them and can't read enough about them. Gotta get off your hiney and practice. Much easier to read and spend, then blame the gun or load when it doesn't work. Horse apples.

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