I bought a Swedish Rolling Block Sporter to keep my full military Swede RB in 12.7x44R company, and of course it has to be shot, and with cast. I have some very preliminary results to share.
Mine slugs 0.323" but with an cavernous neck (0.360") and yards of freebore - well not quite, but 0.600" is a lot.
I chose the Lee Custom molds available from MidSouth - the Karabiner (mine is 0.328" and weighs 230grs) and Maximum (mine is 0.328" and 250grs). Just lubed with Alox, Gas Check added and unsized - left at 0.328".
Brass was made from Starline 45/90 and Grafs 8x56R Hungarian, both sized in RCBS dies. The 45/90 had to have the rim turned to 0.575" and OAL shortened to 58mm (2.275"), the 8x56R just had to be sized (it is a bit short and a bit undersized at the head). Neither were annealed.
I chose the following loads:
13.0 grs Unique with the 230gr in the 8x56R brass - 1290 fps
25.0 grs H4198 with the 250gr in the 45/90 brass - 1520 fps
I'd consider both of these mid-high range (75%) loads.
The Starline 45/90 brass developed a split in the neck due to its thickness and the work hardening of being sized down - no doubt annealing would have been wise, and I will try that next time. The Grafs 8x56R brass fireformed nicely with no splits, but you can see a slight bulge above the rim (not a concern at cast bullet and Rolling Block pressures, e.g. under 30K).
L to R - Starline 45/90, sized, trimmed and fired 45/90, fired 8x56R, Grafs 8x56R, MidSouth 8mm Max, 8mm Kar