IMO, a sand filter should use 1/4 of its capacity in gravel around the laterals.
On TR140 C-3's, the filter I use on commercial pools with multiple filters on a bypass manifold, I use 300lbs of gravel and 600lbs of sand in each filter.
On a single 140 for a residential pool I'll use 200lbs to 700 of sand. This is probably more gravel and less total media than the MFG suggests but I've found it to work very well in service.

hal,
buy your sand from a pool supply house and get sand specifically designed for sand filters. Also don't use just 600lbs of sand. I think the Mfg suggests 950 to 1000lbs in each TR140. That's 20 bags per filter.

See Ya,
Kelly