I am going to be doing some max impact velocity testing using 140gr copper .357 Raptors and hopefully the 175gr brass ESP Raptor.

I have not loaded for such a round with so short a barrel before.

I have the following powders available:

H335, H322, Benchmark

Accurate 2640 and 2230.

Not sure I have any large rifle primers other than 215M. Will they be overkill in such a small case?

Please advise.

Your powder and primer choice are good. You could start with a load recomended for a 200 gr bullet and go up from there. I'll look when I get home tonight and see if I have any loads for those powders. I know I used BLC-2 and maybe H335. My favorite loads were always IMR3031 but much heavier bullets. I'm interested to see what you get out of that 140 gr bullet!

Ball powders tend to make a huge flash in a short barrel.

I have found that 60grs of BL-C(2) has worked well with either the Hornady 180gr SSP bullet or the 200gr flex tip bullet out of my 350 Rem Mag in remington Model 7. It has a 20" barrel though so it might not work as well in the shorter barrel of the model 600.

I wouldn't hunt anything other than varmints with either of these bullets but they are what I can find on the shelves locally. They are accurate as can be though.

I just secured 3 pounds of TAC-supposed to be THE powder for the 350mag...........