Pulling on the memory bank strings and not getting much. I don't even have anything marked in my books as it has been so many years since I shot dad's ol' 99 at deer. Seems like the 150s worked best for us, but since you have some 180s, we'll have to see what we can do.
I found some data.....35-38.5 grains of IMR 4895 with the 180s. Start at the low end and work up. With the 180s, you will be near 30-30 170 grain velocities. With the lighter 150s, you can take advantage of your case capacity and push them hotter than 30-30 loads.
Don't forget to set your OAL to the lands in the bore AND per the rotary magazine capacity. Chances are the 180s that fit in the magazine will be short of the lands.
Good luck.
Steve