If your 3031 is the older longer kernel extruded version, you won't be able to get enough powder in the case to achieve top velocity potential. I hear that newer manufactured 3031 is has much shorter cut kernels of powder and may pack tighter in the case. In any event, you might still find decent accuracy with the 3031 compared to the BL-C2, though the BL-C2 will probably beat it velocity wise. 3031 is one of the few powders I have never tried, and my BL-C2 experience is limited to 55 gr bullets and heavier. Most of my 40 gr loads used TAC over the years, with Accurate 2015, 2200 and H-335 before I switched to TAC.