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Profile crimp
Posted by Murphy on May 26 2005
Airborne!,
Hooyah, from the frog level.
The Redding Profile crimp die is a combination of taper crimp die and a roll crimp die. The roll crimp is more 'crimpy' than a normal crimp die. Normally a taper crimp is used for auto loader handgun rounds that headspace on the case mouth. A roll crimp is normally used on heavy revolver loads, 357, 44 mag, etc, and rolls the top of the brass into the bullet slightly. Profile crimp is both of these to a greater extent. The Lee factory crimp die is more like a roll crimp, actually a reduced diameter ring inside the die that actually forces the diameter of the finished round to be reduced by 'squeezing' down a bit. This will really hold a bullet in the case under heavy recoil. I prefer to use the Profile crimp because it has the capability of being adjusted to give a little or lot of crimp and is not so hard on the brass. The profile crimp seems to be better for magazine fed rifles and the factory crimp a little better for revolvers. Actually some bullets, due to crimp grooves, driving bands etc, will work better with profile crimp and some with factory crimp. In revolvers, the bullet goes forward out of the case under recoil and locks up the cylinder. In the magazine rifle, the bullet is pushed into the case under recoil. There is going to be some increase in chamber pressure if this happens, but mostly we are concerned about the bullet going so far into the case as to prevent it from feeding into the chamber when the action is cycled. Crimping, when it is done is to be accomplished in a seperate operation. Most seating dies have a crimp capability of some extent, but to do this means you are seating and crimping at the same time. That is seat, then crimp then seat, actually pushing the bullet after it is crimped. This is not good for accuracy. The seating die for the 45-70 has a roll crimp in the die. It should be adjusted to seat only, no crimp. Then do all the crimping in the fourth stage, the crimp stage. I use a Redding T-7 press and have all four dies installed when loading the straight sided case such as 45-70 or 38-55 and that makes it a little more convenient. But can be done just as well one die at a time, single stage. Hope this helps. Good shootin'.
Murphy
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