The microgroove apparently came into being in the mid '50s. I believe microgroove is supposed to be better for jacketed rounds, ballard for lead. This is all debatable, though. It's funny, I have a 1980 336 in 30-30 and a 2000 1894 in 45 Colt. The 336 has microgroove rifling and the 1894 has ballard rifling. I shoot lead pretty much exclusively in the 1894 at lower velocities and it's very accurate. I just got the 336 and have not shot it yet.