The Gras was derived on from the Chassepot, and the Chassepot iīve seen a few by now.
To me the Gras is under permit while the Chassepot is not.
No. Itīs not an 11mm rifle itīs certainly a 45 cal one. Iīve slugged a plethora of Chassepot and most come out, groove diameter, at 459-460.
Bore diameter though is normally on the 11,05mm mark.
Iīd be real surprised if the same wouldnīt hold true for numbers of the Gras too as the French never really threw anything away and the Gras is in essence nothing but a Chassepot with a chamber cut for a brass cartridge.
Thus, as i compete with the Chassepot, iīve come to use bore riders of our own design, and these work very very well. Sports a main body diameter of just 11,05mm and then drive bands (4 or 5 of them depending on which of the designs of ours) that measure a full ,460" ( or approx 11,65mm for us metric guys).
The rifling of these guns is just insanely deep. Being all to aware of the ideas to combat fouling and what not, pointlessly so.
Even got a muzzle loader based on the same barrel, a Felix Escoffier 451 jobbie. Sure, barrel looks a little different from the outside but i bet the thing was rifled on the same machines as for the Chassepot.
Sports the same 1:21" twist, same amount of grooves and so forth.
Got several of them standing around but what i campaign for the moment is this rather rare cavalry carbine. Slightly shorter barrel, slightly shorter stock, all brass furniture, different sights and so forth.
Not all that many of these were built and most of them in turn got transformed into Gras rifles.
Then the Felix Escoffier 451 muzzle loader. I presume as sorts of an answer to the British made counterparts, itīs just that the Escoffier jobbie is.. mind blowing. It makes my Whitworth come across as a coarse log.. EVERY damn thing on the gun is "designed", down to the trigger shoe and what not. Way way way lighter than its British counterparts too.
So. There you have it.
The same barrel, from muzzle loading to paper cartridge to brass cartridge. Same gun, if you wish.
Fwiw you might want to explore using duplex loads. A small amount of "mid burn rate" smokeless will make life much easier, not there to enhance performance but.. the smokeless present will kill fouling in its tracks and the barrel in case will handle duplex with ease.