Barrel slides can range between 1/16" up to 3/32" + or - . I like mine thin, around 1/16" or a little thicker, ie: .070". As to width, around 3/8" or so, again + or -. For Hawken rifles, slides are wider and thicker than for longrifles. English rifles about half of what I use for plains, in thickness at least. I use pins in Jaegers.
Slides for longrifles I often make by silversoldering a head on a strip, for example, solid pure silver head on a brass slide. That way, I can set the angle to accommodate the angle of the forestock. I forge my plains and English wedges from steel.