K31 and cast...where to start! LOL!
I will give you 2 pointers that are basically common knowledge among seasoned k31 reloaders:
1.) k31's have short, very short throats. You will want to be aware of how deeply you are seating the bullet. Some bullet profiles will force you to seat them deep into the case. As you know seating a bullet deeper into the case raises pressure. Adjust powder charge at your discretion.
With a given bullet you will want to know what COL will get the bullet seated to where it touches the lands, and then seat it a bit (maybe .010") deeper to avoid initial pressure spikes.
2.) I think most k31's slug at or around .307". A .308" or .309" cast bullet should work fine, so long as the alloy is not TOO hard and you have GOOD lube in the grooves.
~NRA LIFE MEMBER~
~NRA CERTIFIED INSTRUCTOR~