I had once an eye on a gras rifle in 32 ga or 14mm shotgun as they were termed than because 32 ga is close to the 500 BPE case head. so I thought it would be a good action for a sporting rifle project in 12,7x60R 500, an old german hunting cartridge using the 500 BPE case cute down to 60 mm.
have for years now another project with a barreled Chassepot carbine action still for the 11mm Cassepot needle fire cartridge and hope I can move it this year. my idea is to make a teutonic jaeger rifle with this.

as you may know the Gras is a modification of the Chassepot needle fire rifle and most of the Chassepot rifles still in french hands after 1870/71 were transformed into Gras rifles.

the Chassepot /Gras action is very similar to the Mauser 71 action and you can compare the two. the Gras shoots a 25 gramm lead bullet with 5,25 gramm blackpowder and a V0 of 430 m/sec when the Mauser 71 shoot a similar 25 gramm bullet with 5 gramm and a V0 of 425 m/sec. this makes the Gras round the number 2. in power of all military blackpowder rounds after the 577/450 Martini Henry.

the gras have a rich history as a hunting rifle in africa but because most times in the hands of native's this is unwritten.

imho, this are Gras carbines

and this is a Gras rifle

you will find the Gras action having no safety! the only factory made safety on this action I am aware is the safety for the Saxon transformed M 73 cavalry carbine. this was made by reworking captured french cassepot rifles and chamber them for the 11,15x60R Mauser cartridge.
the Saxon carbine have a spring loaded pin on the left side of the receiver going through a hole and block the bolt. the safety is moved with a lever on left side visible on the pics

my idea for the chassepot jaeger rifle is to make some kind of trigger safety.

if your gras is in 32, 28, 24 or 20 bore there is probably enough meat the shotgun barrel can be rifled and you shoot the german blackpowder shotgun bullet cartridge in this rifle. when you give me chamber and barrel dimension I can tell if it possible.