To make 3 bronze nugget you need 2, because the recipe requires 2 metallum and 1 instrumentum, bronze nugget has 2 metallum and 1 instrumentum, making the only spent resource being fuel and a little bit of time. This doesn’t sound balanced, and I wonder if it is intended like that.
If it wasn’t intended, maybe give 2 nuggets instead of 3, which would make it necessary to use flint as instrumentum source, or make it require 3 metallum, which would require you to convert 2 bronze nuggets and for example 1 copper nugget to get 3 bronze nuggets out, aka equivalent exchange.
