I'd try a heavier bullet first. 1680 is significanlty slower than 296 in the 44 bore. In my 44 Mag, there was at least a 170 fps difference, and I see little reason to think that would change. The 1680 needs extra bullet weight to help light the fire. I typically find that a heavier bullet will do more to help a powder that a primer. That doesn't meant a longer flame primer won't help, just that I've had more success getting a powder to act right by adding bullet weight.