The following is based upon the Handloader article by Stransky and Stockwell
and relates my experiences trying to simulate their efforts.
While it is possible to use the 8mm Lebel sizer die to form the brass, I chose not to do so (mainly for logistical reasons). Instead, I purchased the 8mm Lebel form/trim die from Huntington's ($45). This is my first case forming die and fortunately, a very simple one. You simply run the .348 case into the die and remove any brass protruding from the top with a hacksaw and then file smooth. Don't worry about your expensive die, it'll hurt your file before you hurt it. You then full-length size in the 8mm Lebel sizer die. If necessary, you might want to run the cases through your case trimmer to make them uniform, but they most likely won't need much.
At this point you're ready to prime and load.
One thing I noticed is that the formed brass does not have the double shoulder that is so distinctive of 8mm Lebel. This appears to be irrelevant, as the case will most likely obtain this when the brass forms to the chamber on the first firing. Being paranoid, it bothered me a bit the first time, but I got used to it.
Also, the Handloader article mentioned that the rim on the .348 brass is
smaller than the normal 8mm Lebel. This is true, but I experienced none of
the extraction problems they describe in their article. YMMV.