What is the best mix to feed ram lambs and shearlings to grow them to their best potential without the risk of waterworks trouble?

I've always taken the view that the risk of urinary calculi really kicks in when the rams have stopped growing and so need less calcium than a normal ewe ration designed for pregnant/lactating ewes.  We always feed any show ram lambs or shearling rams which we are keeping on with a 50:50, by volume, mix of coarse sheep ration and rolled barley.  Adult rams also get the same mix to build them up a bit after working with the ewes and for a few weeks over the worst of the winter.

Thanks Jacobus, what about sugar beet pellets? good or bad idea?

I believe that sugar beet pellets as well as being high in energy are quite high in calcium, but very low in protein.  I used to put sugar beet shreds in a mix with rolled barley if we had a late batch of lambs needing finishing off inside.  I did so because I thought it would improve palatability and aid feed uptake and therefore weight gain.  One day we ran out and couldn't immediately get any.  The lambs happily ate up straight rolled barley with no effect on uptake or weight gain so have never used them since.