I am developing subsonic loads in my ar-15 for the 458 socom. I had problems with extraction until I cut down the buffer spring a bit.

My current problem is the condition of the brass after firing. It is very dirty, and does not come clean at all in the tumbler. The soft black residue wipes off easy with a scrub pad though. Is this due soley to the cast bullet/lube? The bullet is a plain base design, no gas check. This is enough to drive me to using jacketed bullets only.

Ranb

I have no experience with that cartridge, but it is not normal for cast bullets to make the case black. Sounds like gas residue caused by low pressures and failure of the brass to expand enough to fill the chamber.