It's good for firing 150gr of PELLET powder, but probably not 150gr loose powder loads. The older versions of the Wolverine & USAK were only good for 120gr of Loose powder and I think that is a very good limit if you use loose.

Typically you WILL loose accuracy with too much powder - especially if you're using bullets lighter than 300gr in weight. It's actually a lot easier to over-power the lighter bullets with these fast twist barrels than many people think it is. Since about the Heaviest bullet sold for the .45s are the 275gr PowerBelts, I would say 100gr of loose powder is as far as you can go and expect much accuracy out of your Knight. Work your loads up starting at 80gr & work up to 100gr in 5gr increments and I'd venture to say that the odds are over 90% that your most accurate load will be found in that range.