I think 300gr is pretty much the limit in the .44, if you can push them faster, for example in a 445 Supermag, or the .444 , 330-360gr is about it. I have no experience with the .44, just going by what I've read. Marshall Stanton of Beartooth bullets has done extensive testing of big bullets in the Marlin 444S(1:20) and 444P(1:38), pushed harder, the bigger bullets work in the slow twist, but in the 44mag, 300gr is about the limit, I don't recollect anyone shooting 330gr in em, 300gr XTPs work real good in the 445 Supermag tho which is an easy hand rechamber, but I don't know if the SB1 version would handle the pressures involved which is a good bit higher than the 44mag.
Tim