Plated bullets have there places , in 357 Magnum loads ain`t one of em !!!!
I`m sure most if not all plated bullet manufacturers say to not exceed 1,000-1,100 fps.
The reason for this is the coating is only .005-,007" thick & will start stripping off the bullet either at the forcing cone or rifling trying to get it spinning .
I pushed em (158gr HP)hard enuff to blow the cores out the nose of the bullet.
I feel the HP was punched thru the coating & gave the soft core a chance to slip under upper pressures.
I know I was doing summtin that the plated bullet was not supposed to do & this is not to bash any of the manufacturers of plated bullets !!
They just are`nt for me in my shooting situations ,but they do allow alot of people shooting capibilitys such as ranges that require coated or jacketed bullets & people that just do not want to handle lead boolits.
All of the above is my humble opinion & limited exp. with 158gr. HPs in a 357 mag. shot from a SS GP100 6" barrel never exceeded load recommends for jacketed bullets.
Now , off my soapbox .
If ya gonna use the plated bullets with a slow powder ya need to trim ya brass as close to each other as possible for a consistently controlable crimp .
As you`ve already exp. you can cut em very easily !!! & it takes a little work but ya can get a decent grip with out damageing the coating .
First thing taper crimping won`t work it resizes the entire soft bullet & actually loosens the coatings bond to the core.
I trimmed as closely as possible, deburr well , chamfer with a regular tool ,then chamfer with a VLD tool , this chamfering removes ane rite angels that come into contact & helps flat surface contact with a mild roll crimp.
BUTTT , I had as god results with no roll & slight taper crimp (to ensure chambering) & a load of IMR700x or CLAYS (a fast easily ignited powder).
As mentioned above the slow burners are very sensitive to crimp & pull.
