It's always a good idea to start below where you expect to end. I'd start with 84-85 grs of R-15 and work from there and remember you'll need filler in the R-15 loads.

Definately get a chronograph, best $100-$150 you will spend.

You'll also need to work up a load with IMR4831 as your lot of powder will be different than Butch's. I've had 2-3 gr differences in different lots of the same powder. I now buy an 8lb canister when I have settled on a powder, work up loads again with the 8# and then know I'm safe for a while.

Good luck.