Heaviest I "use" is the 270 gr 429640 HP. I have tested heavier but never had any need for them. Always felt if i needed a 300+ gr bullet I'd be carrying my 375 H&H or 450-400-70.....
Truth is I shoot the Lee TL430-240-SWC in lighter 44 SPL loads or mostly the Lyman 429421 over 8.5 gr Unique for a mild mid-range load.