I have three original FDC barrels,The largest one maybe goes 1-1/8". The smallest being about .60" with the largest being about .65".The longest being about 42+" is missing bout 2 inches as judging from the original front sight.I think it weighes around 4 lb. or so. Oringinal specs say a 4 pound barrel was the rule.some other things to consider weightwise:
The flats only go out 11 inches or so.they taper,no flare[extra metal]
The iron buttplate/trigger guard are forged,much thinner& lighter than a wax steel casting,
on some the wood stock is thinner ,more slender than on guns we see today,A little here, alittle there adds up.
If i can find a Colerain 46' ,.66 cal barrel,take the flare off the muzzle shorten the flats to 11",file 16 flat transition. i can get a 7 to 7-1/4 lb. fusil.
I used the barrel TG stated ,did the above items to,and ended up with a seven pound gun.Whch is on par to originals
I have an R.E. Davis French fusil barrel,48"..62 cal. Which is profile close to originals.1-1/4" at the breech.The finished gun it is on weighes about 8.5 pounds.
Another thing to consider is caliber,a smaller bore will reduce weight.guns from Tulle were of a spcific bore size,+ or -tolerences.
One day i will get some new barrels made to the profile of the best of these barrels.
i hope this helps some.
Alex E.