Unless someone advises against it, I plan to buy the Missouri Bullet Co 170gr cast (
https://budgetshootersupply.ca/product/missouri-bullet-company-cast-32-40-321-170gr-rnfp-1-100-bag/ ) to load with.
Looking at some scans of reloading manuals (particularly the Lyman Cast Bullet Handbook) I hope to use 700x powder as I have a full sealed pound of it I was given 2 years ago and I don't use it for anything else
Lyman shows for 164gr bullet using 5.0-7.5gr and for the 184gr bullet using 4.8-7.3gr of 700x. So I'm thinking a nice mid-range load of 6.0gr for the 170gr bullet should suffice for hitting steel at 100 yards