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What are people talking about when they refer to different grain ammo...?

Discussion in 'General Gun Discussions' started by SilentStalker, Jan 4, 2006.

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  1. SilentStalker

    SilentStalker Member

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    When people say FMR or JHP and refer to different grains in different forms of ammo? I mean what does it refer to? Will someone please explain this in some detail or direct me to some place where I can learn something? Thanks. Please forgive me for my ignorance.
     
  2. Inline_6

    Inline_6 Member

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    It is the weight of the bullet. A 230gr 45ACP bullet weighs more than a 185gr bullet.

    FMJ= Full Metal Jacket (often called "ball")
    JHP= Jacketed Hollow Point

    :)
     
  3. SilentStalker

    SilentStalker Member

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    Gotcha! So, what would be the advantage of having a heavier bullet over a lighter one?? I would assume the lighter grain would be more accurate at larger distances with greater velocities but with the trade off of lighter damage. I assume that a heavier grain bullet would do more damage, be less effected by wind etc. but has a trade off of being shot with less velocity and nto as accurate as a lighter grain. Please correct me if I am wrong as I could be way off or it may be that it is really completely opposite of what I just said. Is there any place I can learn about different types of ammo and what would be better for certain scenarios?
     
  4. LawDog

    LawDog Moderator Emeritus cum Laude

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    http://thehighroad.org/library/acro/acron.html

    That link is to a list of common acronyms used on this site.

    When folks talk about grains, they're talking about the weight of the bullet in a load. Most calibers have a certain range of weight that they'll accept.

    One grain is roughly equivalent to .002 ounces, or .06 grams.

    For instance, the 9 X19mm can use a bullet as light as 115 grains, or up to 147 grains; the .45ACP goes from a weight of 185 grains to 230 grains.

    Be advised, however, that there are specialty loads in some calibres that may weigh more or less than the standard range.

    LawDog
     
  5. LawDog

    LawDog Moderator Emeritus cum Laude

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    A heavier bullet, being slower, has more time in flight to be acted on by the wind.

    A heavier bullet has a more rainbow shaped trajectory, then the lighter, faster bullet.

    Some barrels are designed to stabilize bullets of a certain weight, using a lighter or heavier bullet than the twist is designed for, degrades the accuracy potential of your firearm.

    A heavier bullet generally penetrates the target deeper. There are times when you need to go through 24-36 inches of target, and there may be times when not more than 12 inches is required.

    LawDog
     
  6. MCgunner

    MCgunner Member

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    Then again the longer bullet in the caliber has a better ballistic coefficient and will hold more velocity at long range and be less effected by wind.

    It's more complicated than you might think on first blush.

    There's 16.-something grains in a gram if I remember right.
     
  7. SDC

    SDC Member

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    A grain is 1/7000th of a pound, and you multiply grams by 15.432 to get grains. Lighter bullets fly faster, but may not penetrate as well as a heavier bullet (which can be important in some uses).
     
  8. gremlin_bros

    gremlin_bros Member

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    first off theres nothing to "forgive" you don't know and are admittedly ignorant.
    ignorance we can fix stupidity is up to Darwin and his award winners to fix. i think the information put forth explains the question you asked quite well.
    i for one am glade you asked it shows that you are willing to learn and not just blunder on with no clue as to what your looking at.
     
  9. SilentStalker

    SilentStalker Member

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    Awesome. Thanks for the help guys. This gives me a little better understanding of bullet characteristics and uses.
     
  10. RVSinOK

    RVSinOK Member

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    Great questions and answers! That's what THR is here for - to share knowledge - and I think it is the best source there is. No such thing as a dumb question here, and that's one of my favorite things about this place! :)
     
  11. Jim March

    Jim March Member

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    In handguns, heavier bullets for the caliber are often more accurate, within limits. Handguns are what I know best, so ALL the data below applies to handguns ONLY:

    When we're talking about defensive ammo, the ability of hollowpoint ammo to "expand" is a function of the design of the projectile and it's speed.

    Drive the round too fast, it'll come apart on impact. Or more accurately, it'll expand all right, but then the nose area that's supposed to expand "flakes apart" and is found in pieces in the path of the reduced-weight main slug which is now only slightly wider than in it's original unexpanded state. This isn't optimal.

    Drive the round too slow, it won't expand. Also not good.

    Each hollowpoint (jacketed or otherwise) had a given "speed range" it needs to operate in. With some designs this can be fairly narrow, as little as 150fps in extreme cases...fails at, say, 800fps ("feet per second"), expands nicely at 900, fails again at 950.

    Bullet velocity is affected by bullet weight for the caliber, the powder charge behind it and the barrel length...the shorter the barrel, the slower the bullet, anywhere from 25fps to 50fps difference per inch of barrel as long as we're talking about handgun barrel lengths and ammo designed for handguns...stick handgun ammo in a rifle and in some cases you'll get a major speed boost, in others it will be minor.

    So what does all this mean?

    If your gun's barrel is abnormally short for the caliber, you may want to consider a lighter bullet. In a compact 40S&W gun with a 3" or less barrel, I would prefer a 135gr load, or 155 max. In a 5" barrel "police handgun size" piece the 155s and 165s in that caliber have merit, but in a 40S&W carbine (16" barrel) I might consider a 180gr heavyweight.

    Take another case: you have a 38Spl revolver with a 2" barrel (a "snubbie"). Most of the best rounds for this gun run from 110gr to 135gr, and in "+P" flavor (meaning a bit of a speed boost over normal ammo, up to 10% over normal maximum pressure). There is one exception: the 158gr plain lead hollowpoints with NO jacket are an old design but work OK at low 38spl+P snubbie velocities. The plain lead is slicker than copper or brass so it goes fast for it's weight, and the plain lead hollowpoint opens faster than jacketed hollowpoints. BUT it's speed limited, drive it too fast and it'll come apart due to no jacket. It would have been discarded long ago except it's "tuned" just right for snubbies so it's still a common ammo type for these guns and a damned fine choice.

    In a 4" to 6" barrel 38Spl I would stick with various jacketed rounds esp. the Speer Gold Dots in 125gr/135gr and the Winchester Supreme 130gr.

    Semi-auto guns don't usually do too well with lead ammo and usually drive rounds too fast for lead hollowpoints to cope well. So the usual "short barrel should be linked to lighter rounds" rule of thumb tends to apply across a range of calibers and JHP types. Still not universal and the projectile design matters a LOT...

    If you have a barrel sized "normal to long", a heavy or superheavy round will penetrate deeper all things considered. If you're loading a round designed NOT to expand (such as a "hardcast" lead slug with no hollowpoint or a full metal jacket type) for hunting or self defense against dangerous animals, you'll often want the heaviest slug you can get for the caliber.

    Example: a guy with a 44Mag 5" barrel might use 200grain JHPs for home defense loaded a bit on the mild side for reduced recoil, but when he walks the woods in bear country he'll have the same gun loaded with 300gr or more (up to 320/325) hardcasts driven as hot as they can go. The 200gr JHPs would hurt a human more with their wide but "shallow" wound channel of up to about 12" or so but those big hardcasts at full-house power will punch 40" or more deep and reach a big beast's innards or blow up it's shoulder or spine.

    In this sense, the bullet weight is tuned to the mission.
     
  12. SilentStalker

    SilentStalker Member

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    Thanks for all of the info. JIM! That was very informative and man did you provide a lot LOL. Keep it coming.
     
  13. Justin

    Justin Moderator Staff Member

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    Consider taking an NRA course in firearms. There are probably multiple instructors near you. The classes shouldn't be terribly expensive, and they'll go over all of the basic stuff, as well as allowing you to get some range time with more than one kind of gun.

    Check here:
    NRA Training Courses
     
  14. trickyasafox

    trickyasafox Member

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    if you want to play with a cool tool to learn a bit about how balistics work check out this link:
    http://www.norma.cc/htm_files/javapagee.htm

    its a ballistics calculator. you can adjust some of the properties and see how the trajectory is affected. might be interesting to you :)
     
  15. palerider1

    palerider1 member

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    FMJ means full metal jacket,,,,meaning that the entire lead bullet is encased in brass. JHP means jacketed hollow point meaning a lead bullet that has a copper jacket around it except for the point which is hollow exposing the lead core,,,,,,,,,,,,,,,,,,,,,cant give you more then that since i'm f-----ng tired and cant go any more,,,,sorry,,,,,,,,

    have fun,,

    remember, no question is a dumb question unless you dont ask it. i have been shooting for over 30 years and i always have questions....guess thats the way it goes...... i always try to learn something every day

    palerider1
     
  16. Lebben-B

    Lebben-B Member

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    Now to muddy the waters a bit. Grains are not only an expression of a given bullet's weight but of it's length as well. Simply stated, the caliber of a bullet is it's diameter. This diameter is constant; you can't change the diameter without changing the caliber of the bullet. Since you can't increase the diameter, a heavier bullet must be longer, because the added weight must go somewhere.

    Mike
     
  17. Carl N. Brown

    Carl N. Brown Member

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    7,000 grains to a pound, 437.5 grains to an ounce.

    About 1540 grains to a kilogram, so 15.4 grains = 1 gram.

    Normal adult aspirin tablet is 5 grains or 0.325 grams (325 milligrams).

    I memorized these years ago for quick'n'easy rule'o'thumb work.

    American bullet and powder charge recipes use grains.
    European bullet and powder charge are usually in grams.

    We are all ignorant until we learn something new.
     
  18. Jim March

    Jim March Member

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    Lebben-B is correct: heavier means longer for a given caliber, which means more bullet in contact with the inside of the barrel, which is why heavyweights are often more accurate.

    This is NOT universal however and other factors affect accuracy. For max accuracy, the barrel's rifling twist rate needs to be matched to bullet weight.

    This latter link to "twist rate" matters more in rifles than handguns...with rare exceptions, most handgun makers all stick with the same twist rate for a given caliber.

    Twist rate is measured in how many inches to make one full twist.
     
  19. mrmeval

    mrmeval Member

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  20. JMusic

    JMusic member

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    Good to have you onboard Silent Stalker. Subscribe to some "gun" magazines and be sure to follow safe firearm practices. You will find a wealth of knowledge here, welcome.:)
    Jim
     
  21. Snagglepuss

    Snagglepuss Member

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    This was a question I was meaning to ask. Thanks for the original post and all the answers. I am now somewhat less ignorant:p

    So... is the FPS related to the amount of powder in the round, the type of powder or both? So when I see +p or +p+ that simply means an increase in FPS?

    I recently bought a 10mm commander. I visit a lot of forums and see talk about the "full strength" vs. the "new weaker" loads. There is a lot of talk about the 200g vs. the 165g or less. Then comes all the talk about FPS. It gets confusing. I just ordered 1000 rounds of 165g JHP 1400fps based on reading the conversations of others. They all seemed pretty excited about this load at the price. How would this load be classified? Hot, watered down etc.

    I know these are a lot of questions but since the replies to this thread have been so accepting I though I would "free associate" and get all my questions out. Thanks in advance.:confused: :confused:
     
  22. SDC

    SDC Member

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    Neither, really. "+P" or "+P+" just means that it's a round that's loaded to higher (P)ressure levels, and that USUALLY means a higher velocity, but not always.
     
  23. Snagglepuss

    Snagglepuss Member

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    So what does "loaded to a higher pressure" mean? What then is the advantage or reason, if any, of buying +p or +P+ rated ammo?
     
  24. Dave R

    Dave R Member

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    Higher pressure means a bigger boom in the cartridge, pushing the bullet faster. It also means the fired cartridge is trying harder to blow up your gun. People choose +p or +p+ ammo when they want a more powerful round in their gun.

    The load you describe in your 10mm, 160 gr. at 1400fps, sounds like "full power" to me.

    In case it wasn't clear, fps stands for "feet per second", and measures how fast the bullet is going. Just to calibrate the scale, as it were, the speed of sound is about 1,150 fps.

    To compare your 10mm load, the military .45acp load is a 230gr. bullet moving about 850fps. So your load has a light bullet moving a lot faster. Its a more powerful round than .45acp.
     
  25. Vern Humphrey

    Vern Humphrey Member

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    Not quite. Wind drift may be calculated by (time of flight in air) - (time of flight in a vaccuum) X wind speed. A bullet that loses a lot of velocity will drift more than a bullet that retains its velocity, regardless of actual velocity.

    With bullets of equivallent caliber and shape, the heavier bullet has a better momentum-to-drag ratio and will drift less. This is why target shooters went from 55-grain bullets in the 5.56X45 NATO to heavier bullets -- and the military followed suit. The heavier bullets were less subject to wind drift at long ranges and retained striking energy better.
     
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