Sunday, March 20, 2011

357 Magnum Cast Bullet Crimping

A short note on the roll crimp used for cast bullets:  Nothing in casting and handloading works for everyone, for all guns, for all reloading presses and in all instances.  Crimping is just like that.  You will have to adjust a bit, but crimping does affect accuracy and is important.

I do know the Lee crimping dies and the Dillon Square Deal B dies do work with these adjustment specs (note: the Lee FCD can cause problems. For accurate cast bullets that are oversize at .360 diameter, a regular roll crimp die works best.): 

Crimping cast boolits without a groove, or crimping on the driving band:  This takes pure experimentation.  The Lyman 358-429 crimped onto the front band works well with a light roll crimp.  It's important to crimp enough so the bullets don't jump out of the case due to recoil, and not to much crimp or it will ruin accuracy.

The 700X and HP38 loads in the Most Accurate Boolits and Loads Chart have a medium crimp.  The 700X 5.1 load and all the H110 & 2400 magnum loads have a heavy crimp.

What does this mean?  First, here's how I zero the crimp:

  1. Back out the crimp die
  2. Size a fires 357 magnum case
  3. Place the case under the crimp die and raise the ram (don't use a flared case)
  4. There should be no contact between the crimp die and the mouth of the case
  5. Holding the ram up, Screw in the crimp die until it make firm contact
  6. Now the crimp is  zeroed
Once you are at this point, lower the ram and screw in the crimp die to the crimp needed:
  • Light crimp = 1/2 additional turn of the crimp die from zero
  • Medium crimp = 3/4 additional turn of the crimp die from zero
  • Heavy crimp = 1 additional turn of the crimp die from zero
This isn't how everyone does it, so this terminology isn't universal.  Most all non-magnum loads work well with a medium crimp.  The magnums and the non-magnum powder- near-max-pressure loads work with a heavy crimp.  For example, 5.1 grains of 700X works best with a heavy crimp.

Bullet diameter plays an important factor with the crimp setting.  Recently, with full size .360 diameter bullets, and using a Lee seating/crimp die, a light crimp proved to work the best.  

The 148 wadcutters also work well with a medium crimp.  I've not been able to produce good results with a light crimp on a wadcutter as many recipes or tips advise.  It's worth a try if you are shooting a full wadcutter.  Like the opening said; nothing in casting and handloading works all the time.

No comments:

Post a Comment