Maybe I can shed some history on the 375 cal, 350 gr. SMK. fired from a .408 CT case.
Seirra made a Version 1 bullet, and this bullet was found to "distort" when pushed passed 3000-3050 fps. There were a few given away as free "trial bullets", and quite possibly some are still floating around. I can imagine this thing absolutely Blowing-Up on the near shoulder of any game animal. It was very soft, thin jacketed and just looked for a place to come apart. This bullet was to be shot at paper only to determine bullet stress limits. That is all.
I want to stress....These were never intended to be sold, and never were. These were prototype bullets, to be used only for inital data feedback to Sierra. They were only delivered to certain selected individuals.
It was decided to install a thicker copper jacket, hence V.2 and this version exhibited the same results at 3150-3200 fps. It was better, but in no way acceptable.
Version 3 was ordered and received. This sample had a specially ordered copper alloy jacket which was also thicker yet. It also resulted in about .002" longer bullet length just due to the thicker jacket. This bullet has held up well at all speeds, and testing was completed in late Fall of 2007. Delivery was just taken on the first shipment of 250,000 pieces on May 8, 2008. A full 1 million pieces are scheduled to be delivered before Jan. 1 2009, in 3 incimental shipments.
My barrels are set up to shoot 350 gr. solids with a 1x11.5 8-groove twist and at 32 inches long. Standard COAL gives a .007" jump to the lands with the solids using that barrel. That is perfect for the solids. When shooting the SMK, watch, and pay attention to the land jump. It's easy to seat it overly deep, and accuracy will go South. It actually needs to be longer than standard COAL due to the vast difference in ojives from it and the solid.
That is my experiance,