It's 3031 for me.
Same here. At the moment, it's my powder of choice with the 'heavier' loads in modern .45-70's. To date, some of my best results have been with IMR 3031 and the Speer 400gr FN. With some of the results 303carbine has obtained using IMR 4198, I've loaded up some Hornady 350gr FP's,Speer 400gr FN's and 405gr Rem's with it to test.Works good for me as well.