How important do you think "crimp" is?

Discussion in 'Guns - Blackpowder' started by bootshowl, Oct 9, 2009.

  1. bootshowl

    bootshowl New Member

    Messages:
    2,288
    State:
    Indiana, J
    With the newer crimp dies Lee has, it's nice to be able to put a really good crimp on a round. But I caught myself wondering if it has adverse affect if too heavy with a fast powder in a pistol round? Previous experience has shown me "stringing" with older seating/crimping dies if the crimp was too light.
    Was wondering what some other loaders might think.
     
  2. flathead willie

    flathead willie Well-Known Member

    Messages:
    3,241
    State:
    Virginia
    Crimp is very important. Remember the trouble I was having with my .45 ACP last year? It was because of the ammo I bought. They were crimped too light. Firing the first round caused the lead in the rest of the mag. to sink back into the cases and made the gun jam. I threw that ammo away and the gun works just fine now. The crimp is the first thing I set on my loading dies. Too much crimp also damages the cases and causes high pressures.
     

  3. bootshowl

    bootshowl New Member

    Messages:
    2,288
    State:
    Indiana, J
    When yer bullet goes deeper in the case, the pressure increases also Billie. And if yer shooting a revolver, bullet creep forward, will jam the gun. So I know it's important.....But these new Lee dies will let you crimp without crushing the case. What surprised me was, with a recent box I loaded, I ended up with two points of impact. Then realised, I had adjusted the crimp die for a tighter crimp as I was loading that box of shells. That would imply that a tight crimp increases pressure, or somehow effects the outcome?
    The only way to adjust the die is by half turn, or full turn etc. I was just surprised that the amount of crimp, seem'd ta have such a dramatic effect. Instinct tells me tight is better than light. So from now on I'll make a record of how much crimp I put on the rounds in "turns", and try and make my loads more uniform that way.......
    Unless anyone has a better idea?????
    :big_smile:
     
  4. flathead willie

    flathead willie Well-Known Member

    Messages:
    3,241
    State:
    Virginia
    I'm not familiar with Lee dies. I used RCBS. mine have an adjusting ring that can be moved in fine increments, and a set screw locks them in place so they remain the same time after time. It took awhile to get my 30-30 die set right. Too much crimp and I only get one reload out of each case. Too little and it messes up the head spacing.
     
  5. NJ CLAD

    NJ CLAD New Member

    Messages:
    196
    State:
    Arizona
    It would take a great deal of crimping force to affect the pressure of the round, especially in any gun that was not a revolver. The purpose of a crimp is different in different kinds of firearms. In a revolver, the crimp is for 2 separate purposes; one to keep the bullet in the case under recoil, and the second reason is to insure proper ignition. In a revolver the bullet makes a very large jump from the cylinder to the barrel, so a uniform fairly heavy crimp allows the case to build some pressure before the bullet moves out of the case. This in theory allows the powder to burn uniformly. In any other firearm, the bullet engages the rifling after just a few thousands of an inch, thus creating pressure to provide uniform ignition of the powder. (remember chemestry 101, as pressure increases temperature rises) More pressure equals more heat, thus the powder can burn faster or slower depending on the heat generated in the system. The only purpose of the crimp in an auto loading firearm is to keep the bullet from being pushed in during recoil, as the bullet strikes the front of the magazine. In a revolver one needs a heavier crimp than in any other gun. But remember that too heavy a crimp will deform the bullet, and cause accuracy problems. In a rimless cartridge, like the 45 ACP, too much crimp will affect head space, as in making it to much and may lead to misfires, with a rimmed case crimp has no affect on the head space, as the head space is controlled either by the rim or the case shoulder, never the case mouth.
     
  6. TJD

    TJD New Member

    Messages:
    258
    State:
    Missouri
    I had a lot of trouble with re-loaded 45 ACP cycling in my 1911. That is until I added a Lee Factory Crimp Die to my Dillon press and all the trouble went away.

    Bullet pull is also affected by the amount of sizing the case gets. Case thickness and the size of the "Sizing Ball" can all change the amount of bullet pull. If these factors are ok then run some tests.

    Crimp does affect the way wheel-guns shoot. Load several rounds with a light crimp. Load some rounds with Med crimp. Load the same amount of rounds with a heavy crimp. Make sure that the only differences in these rounds is the amount of crimp. Carefully test fire them. Allow your gun to tell you which one it like.