Back around 1978, I bought or traded for a slightly used Zouave Repro. Marked Antonio Zoli and Italy on the Barrel, and get this, on the trigger guard it is marked "Sears, Robuck & Co."
It should be rifled. Although if really made in the 1950's there's a possibility of anything. The Centenniel of the Civil War was big doins here in the East and quite a few folks got into skirmishing. If the guy were to say it was from 1965, I'd find that a bit more credible. (In the 1950's you could buy originals cheaper than the Italians could make them.) I remember my dad and uncles in the mid 1950's buying old percussion long rifles at farm auctions for $10 to $15 and shooting them later in the day. (I was only 6 or 7)
My Zouave, is actually quite pleasant to shoot with PRB's and 60 grains of powder. (Very close to the original military load) I have read that it was the best engineered muzzle loader gun of the war era, but was never really issued to US troops.
While it seems pretty accurate, The big wide military style sights are "verstutzed" and not capable of really fine accuracy. (Verstutzed, a Pa Dutch term for "screwed up", or "not right" The term can also apply to humans.) I actually started my son at age 8 shooting the Zouave with 30 grains and PRB's, he did pretty well. I am basically a flint lock shooter. The percussion thing is not real popular here, but the gun is heavily made and would be my choice if I ever got a chance to hunt for bear or elk.
There were several different Italian manufacturers making Zouaves. Even CVA sold a Zouave for a year or two back around 1978. Mine has a one piece barrel with welded bolster added and a breech plug screwed in. Another brand used a one piece breech unit screwed into the barrel with a pipe nipple type union. That one always struck me as being a weak system. I'd check to see which it is. If the first type, there will be no visible line around the barrel about 1 3/4 inches from the rear of the barrel. Obviously, the weaker system will have a visible joint line running around the barrel at that point. When I mean a pipe nipple, I really mean a pipe nipple. The breech and barrel both have female threads and a two inch adapter is threaded with male threads on both ends and is screwed into both parts to make the union. The barrel is actually in three pieces right where it is subject to the most pressure. Some times you can feel the patch and jag hang up on the place where the barrel and the adapter meet in the bore. If it is one of those weaker barrels I would never shoot over 60 grains in it. But hey, it's your face. If it is the good one, you can shoot up to 100 grains no problem.