My first loading tray was made by my reloading mentor back around 1972. It consists of two 3/4" pieces of wood stacked on top of each other. Apparently, he drilled 50 holes that go through the top piece and half way through the bottom piece. He then cut small slots in the top piece, 2 on each end and then drove large headed roof nails down through the slots into the bottom piece of wood. This allows the top piece to slide back and forth and the nails act as stops. When you slide the top one way, both sets of holes line up and it is good for longer rifle cartridges. When you slide the top the other way, the the holes in the boards are offset and the holes are only 3/4" deep and it works for pistol cartridges.
I also have 2 plastic trays that I purchased over the years. I too use a single stage Herter's press and find the trays very helpful. Right now, two are holding some 45/70 rifle brass and the third is holding some .357 mags.
