light load .223 Rem
I use the RCBS 55 SP-GC with 7~8.0 grains of Unique..the lighter charge gives you 1,800 FPS Muzzle Velocity. I find you must seat long so that the bullet just engages the leade when chambered. This caliber with cast is quite finicky when it comes to accuracy. Also shoot the .22-250 with it and have had better luck.