TOW sells Bouchards book on the Fusil in New France, it is paper back and under 15 bucks and has a lot of info on contract lengths and such it covers the period that Tulle made guns under contract for the king, there were Hunting guns, Buccaniers and Grenadier muskets, this booklet covers 1691-1741 it offers a lot of help if trying to find parts/barrels/locks which can be modified to meet the specs so to speak,and it is infered that there were some exceptions to length of barrels at times.