.358 Ultra Mag Imp. Fireform

Discussion in 'Reloading' started by USCGLongBow, Jun 6, 2014.

  1. USCGLongBow

    USCGLongBow Well-Known Member

    Jun 6, 2014
    I'm waiting on delivery of a Custom 358 UM Imp, and prepping the Brass for Fireforming. I thought I would open this up and get people's opinions on a couple things.
    First, does anyone have experience fireforming Ultra Mag Brass? I know it's a harder alloy than standard Brass, and the sidewalls are much thicker, but I can't find a published good start load for Ultra Mag. I saw on another forum, one person's best guess was 20gr of pistol powder with Cream of Wheat, but he had never actually fireformed Ultra Mag brass so it was just a guess based on other mags of around the same size.
    And my second question is a little in left-field, but I was playing with the idea of loading some low pressure loads for plinking or when the kids shoot the gun later. I had also thought possibly using them for the second load down the barrel to ensure the brass is completely formed before going up to published 65,000CUP. I'm thinking something with 158 or 180gr .357XTP over a fast powder. I have some old manuals that say around 30gr of SR4759, but I was wondering if anyone has ever played with this combo on 358UMT. I was hoping to develop a reliable load around 35-45K CUP but I don't currently have a pressure box, so just educated guess.

    Well love to hear your ideas.
    Last edited: Jun 6, 2014