The safest way to get reduced loads for rifles is to use a small charge of a very fast pistol powder, like Unique or Bullseye, or better yet, use Trail Boss. Trail Boss is safe for all rifles when the case is filled to a capacity of between 70% and 100% of remaining space after the bullet is seated. IMR is very clear that Trail Boss
must never be compressed.
IMR explains how to work up a load here:
http://www.imrpowder.com/PDF/Trail-Boss-data.pdf
I bought Trail Boss to fireform my cases but I've found that it's really a great powder. It produces loads in my 204 at 75% fill that are so quiet you don't need hearing protection.
I produces loads in my 7mm-08 that are an absolute pleasure to shoot. It really tames the recoil of the 7mm in a handgun.