My old Sierra manual goes well above that, up to 42.4gr.  I see their newer one does too.  Hornady 3rd goes up to 40.  4320 was one of the first powders I worked with.  I wound up kicking the bolt of my Madsen open because the data I used was developed in Winchester brass, but I was using GI brass.  And, I didn't start low  & work up, just picked a number a couple steps below max.  Not enough numbers below, it turned out.