Managed to get a game of Nach Paris! (a Franco Prussian Fire & Fury variant) in on Thursday as the Prussians. A great game but it did reveal the issues around modifying one rule set for another period. Some of the key mechanisms in Fire & Fury work on the basis of equivalent ranges for musketry in the American Civil War. Clearly this isn't true of the Franco Prussian war where ranges and fire power differed significantly between the opposing forces. So do you introduce differential ranges and, if so, how do you deal with the "retreat beyond enemy musket range" results? The Fire & Fury mechanics clearly have a level of abstracting and thus introducing a new variable can create some problems which aren't immediately apparent.
As it was the game was great fun and the weapons issues have been taken away for a bit of tweaking. Unfortunately the result was relatively historic with a French "victory" but I'll put that down to a lack of aggressiveness on my colleague's flank (of course a lot fewer duff dice rolls on my part might of made a difference too!)