Mines nothing fancy. Just a SS laminate with a simple bedding job. Factory barrel but IMO a really good one compared to some ive seen.
63gr of Reloder7 or 56-60gr of N120 with a variety of 300gr bullets shoots well in mine. 458s usually shoot better than .452s but not always. Getting a good sabot to bore fit is the most important thing and let the barrel cool between shots.
60gr N120 and a 325gr FTX in a MMP Orange is one of the best shooters in mine but it is a little bit brisk. Not bad but you know you pulled the trigger.
Im not a big fan of the "book powders" but they do just fine for many people.