Depends. I've fire formed using the cream of wheat method(except I just use tissue paper). That forms the case but leaves the neck id small, yet large enough to run over an expander mandrel for turning. The doughnut gets pushed to the outside and is turned off when turning the necks. Works very well. Many people prefer this method over all others. There's certainly more than one way to skin this cat but neck turning is the simplest of machining operations. It does however, require attention to detail to do a very good job. A few things that cause problems with consistency are the mandrel flexing, the cutter flexing and the cutter body getting hot. Another is too tight of a fit of the case on the mandrel, causing excessive heat and potentially galling of the case neck brass to the mandrel. Too loose is even worse when it comes to consistency. Part and tool deflection are best dealt with by taking light cuts or doing them in two or more passes. Heat just has to be managed. The cutter assembly getting hot can make a significant difference in the final dimension.