Crimping of Drive Band Bullets
Crimping is normally not required with a drive band bullet because the brass
springs back slightly between the drive bands when the bullet is seated. See the
illustrations of a sized case and a case with the bullet seated. The ripples in
the case are clearly visible. This acts as a multiple crimp but has great
precision because the variables from cartridge to cartridge are held to a
minimum. When a normal crimp is applied to a case, varying case lengths, however
small, will cause the crimp to vary and bullet pull weight will vary also. In
some cases, applying a crimp will actually loosen the brass slightly just ahead
of the shoulder. Should you find that a drive band bullet moves under recoil,
first check that the case neck is sized down as it should be, then check that
the sizer button is not over size and, if both are within spec, only then should
a crimp be applied. Make sure that the crimp falls between two drive bands.
To determine if the die set is in spec, two experiments are required. First you
must check the body of the sizer die and secondly the sizer die button.
1. Remove the button assembly from the sizer die. Size and load five cases that
have previously been prepared, sized and primed in the normal way. Do not
apply a crimp and measure the C.O.L. carefully. Load as many into the magazine
of the rifle as it will accommodate. Fire all but the last one. Load the
remainder of the ammunition on top of the one remaining in the magazine and fire
them. Measure the COL of the remaining unfired round. If it has changed, the
body of the sizer die is over size in the neck area or the case necks have been
trimmed too thin or you have a monster recoiling rifle that needs a crimp. This
is unlikely. If the COL has not changed, you obviously do not need to crimp.
2. If the first step shows no crimp is required, repeat the sequence but with
the sizer button re-installed. If this firing sequence shows a difference in
COL, the sizer button is over size. Spin the button down until the case holds
the bullet effectively.
The same experiment can be done with double rifles by loading both barrels,
firing only one side and checking the unfired round in the other barrel.
GS Custom Bullets, situated in Port Elizabeth on the East Coast of South Africa, manufactures solid copper, turned, monolithic hollow point bullets for
hunting and sport shooting. These bullets are used by hunters on several continents, hunting from the smallest of antelope to the largest of dangerous game,
using the smooth HP bullet, as well as the more popular HV, FN and SP bullets with the patented drive band concept. GSC bullets are configured for the
highest possible ballistic coefficients. SP bullets are mainly used for sport shooting. All GS Custom Bullets are coated.