timber boss,
have shot a 25 WSSM for years and years, in a bolt gun. Also dabble with AR's. My opinion is that the gas guns operate best with the medium powders, say around 748 , CFE223, 414 and so on. The 25 in a gas gun may be totally a different animal than in a bolt gun. Perhaps someone with hands on with the AR will chime in. By the way, the 75 VMAx worked best for me with Rl 15. I think 17 is gonna be too fast anyway!
Hope this helps, jsut my 2 cents adjusted for inflation!
Greg Harrison