sorry for all the questions

Discussion in 'Reloading Room' started by joey1117, Jan 26, 2015.

  1. joey1117

    joey1117 Supporting Member

    Ok so first I am sorry for all the questions ..however I just got 500 45 cal 200 grain and 500 115 grain 9mm these are powder coated and was told to use the lead round nose data ...SO that being said ...and I cant post grains of powder on here ...why does it take more powder to push a lighter bullet ? Im about 1 1/2 grains more than I was on the 45 when loading a 230 fmj and about 1/2 grain more when loading a fmghp on the 9mm ....just seeing if there is an easy answer
  2. Grant

    Grant Member

    The short answer is that pressure doesn't build up behind the lighter projectile as easily, therefore more powder is needed with a longer burn to get bullet speed where it needs to be. Way oversimplified of course.

  3. Joey can't swear to it but I believe it has to due with the lead bullets being a little bigger and the drag in the barrel, typically a 9mm FMJ is .355" dia. where as the lead RN in .356" dia. from what I've read lead is bigger to keep pressure from blowing by. But I could be off base on this.
  4. Rachgier

    Rachgier Administrator Staff Member

    Now I'm going to hazard a guess, even with my own newbish reloading skills.

    It's a velocity and pressure thing. Smaller bullet requires less pressure to overcome inertia. Since the bullet moves further faster, the pressure from the charge is dissipated sooner, therefore a larger amount of powder, or faster burning powder, will increase the pressure, which in turns increases the velocity of the projectile.

    Larger bullet, more inertia, less of a charge required because the round accelerates slower.

    Somebody feel free to smack me if I'm wrong.
  5. moona11

    moona11 King of you Monkeys Lifetime Supporter

    Here is all I know. I follow what the books tell me to do. I use the kiss method and don't over think it. To little or to much = bad day sorry for not helping
  6. joey1117

    joey1117 Supporting Member

    I checked the data against 4 different sources .....they were all pretty close to each other then I backed down 10% to work it up ..just made my mind start to thinking ......will test shoot some tonight
  7. cross+hare

    cross+hare Member

    .d all of the above.
    Less weight less pressure.
  8. Branth

    Branth Member

    Grant's got it right. Lighter bullets get moving faster, so there's not as much pressure behind them, so they can take more powder.

    Don't feel bad about asking questions - It's the whole purpose of a forum, after all.
    Last edited: Mar 5, 2015
  9. ajole

    ajole Supporting Member

    NE Utah
    That's also why lighter bullets generally go faster, you are using more powder, without getting TOO MUCH more pressure.

    You put that same large amount of powder behind a heavier bullet, pressure builds up, and blows up.
  10. FlashBang

    FlashBang I Stand With Talon Lifetime Supporter

    You can also increase or decrease pressure by manipulating the bullet pull out threshold via crimping light, medium, heavy, or not at all. :)

  11. Bull

    Bull Just a Man Supporting Member

    Or how deep they are seated.... Or set out against the lands.... IINM...
  12. noylj

    noylj Member

    I think the confusion could be thinking about the same velocity. It probably takes more powder to get a heavy bullet up to the same velocity as a light bullet, but you'll notice that the velocity goes down as the bullet weight goes up, since pressure must be maintained and not velocity.
    Would you really expect to pack MORE powder into a case with a heavier, and, therefore, longer bullet and not have pressure be higher? Can't you imagine the pressure rising much faster for a heavy bullet than for a light bullet? Remember, if the bullet does not move, you have a pipe bomb on your hands--and a heavy bullet has more inertia than a light bullet.
    And don't compare 9x19 to .45Auto, as the max pressure is quite different for the two cartridges.