I use pure lead, but most of my spoons are 3" and under. I can understand the thought and concern for something less forgiving in a larger version, but it isn't a factor with these smaller spoons.
The largest ones I've made were 4" long but those big ones can be done with bigger tubing. They are just copper and brass plumbing tubes cut to length and semi flattened in a vice. I then crush one end completely shut and pour lead in them before crimping the other end. (if that makes sense)
More jigging spoons made from brass tubing that's been semi flattened and filled with lead. The shiny scales were done using a sanding cone on a Dremel tool.