66/74 would have started off as an 1866, a Chassepot. They were a needle-gun using a consumable cartridge. You are NOT going to find any of those!
But it was converted in 1874, so it would have been converted to the Gras cartridge. Gras rifle was just a Chassepot action converted where necessary to a centre-fire.
The 8mm Lebel cartridge was based originally on Gras brass shortened about 9mm and necked. If you are willing to put up with short rounds, you can open up Lebel brass (available in bags from Trade-Ex), seat your .43 slugs 'way out and have a go like that.
Otherwise, you are looking at buying very expensive casings for about $3 a pop.
OR you can make them by opening-out .348 Winchester casings. You could need a lathe for part of this job, depending on your chamber. Rims can be given the correct (required) bevel with a lathe or with a cord-drill and a file and a huge amount of patience.
For some reason, I get the idea that you MIGHT be able to use 32-gauge shotgun brass for sizing down for the Gras casing. Magtech makes it in Brazil, Will Bilozir stocks it in Alberta. He is at most of the gun shows out West; his web address is bilozir dot net and after that I'm lost.
RCBS makes dies, of course, in their 55000 series. Trade-Ex MIGHT have them in stock. They have a LOT of weird stuff!
Bullets you will have to cast, although you might find someone who makes them. They are a .43" slug, over 300 grains. Lyman makes moulds but they are shockingly expensive, close to 100 bucks by the time you get the blocks and the handles. Last forever, though, if you are careful.
I am shooting a .43 Mauser and I'm using bullets cast from a LEE .459-405 Hollow-Base mould, which is about $30. They are 'WAY too fat but a friend made up a .446" sizer with a taper reamer, using a chunk of 7/8x14 threaded rod. Works fine. Same mould works great for a Martini-Henry, too!
"Text Book of Small Arms - 1909" gives the following for the Gras cartridge:
Length: 2.99 inches
Weight: 676 grains
Bullet: hard lead
Length: 1.063"
Diameter: .433"
Weight: 386 grains
Charge: 81.32 grains Black Powder
If you want Smokeless ammo, you can go as heavy as 30 grains of SR-4759 with a 380 - 400-grain bullet but NO HIGHER. This will duplicate original ballistics and pressures.
Also, your bullet diameter is close enough to a .44 revolver that for short-range loads you might think about using a .430 pistol slug. Moulds are cheap, Lee makes them and if they are soft enough (use pure lead) they might even upset if you back them up with FFFg or SR-4759, both of which are fast. For short-range ammo, try 50 grains of Black. Do NOT overload; these are NOT a strong action.
They were made from 1866 Chassepot carbines from 1874 until the supply ran out, then supplemented by fresh 1874s of new manufacture. In the French colonies, they could have been used as late as Viet-Nam. I saw a photo of one, taken in Algeria or Libya about 5 years ago, still being carried. I have NO idea where he got ammo!
Value: I have no idea. What's it worth to YOU? THAT is its value. Dollars aren't everything.
Hope this helps.
