Well.......................... If you have a Business Plan, a financing source, and think the demand is there - Go for it.
Keep a few things in mind, however.
PROJECT: Making BOTH a rifle and ammo in a long un-used ( 120 years) chambering; AND the ammo MUST be safe in firearms up to 150 years old, made of the not-so-strong steel (or most likely iron) of that time.
First, since no one like to dance by themselves very much, both firearm and ammo would most likely have to be made by the same manufacturer (not too many such around any more, see my first comment, above).
Second, any sane manufacturer ( AND their Cost Anlysis Team) would look at several issues:
* Low/no demand for .15/.16 cal (4mm) rifles - especially in the light of the existance of modern .17 cal RF arms.
* Existing 100-150 year old firearms so chambered of very questionable strength/condition - iow, LIABILITY.
* Design/tooling costs involved in startup for new/different arms/ammo.
* AFTER ammo production $$$, obtaining SAAMI or other official sanction/status for the new ammo brand.
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