The Zuave replicas were made to be used for re-enacting Civil War Battles. They have round barrels, and the Barrel walls are pretty thin. This is not like an Octagon Barrel chambered for the .58 Cal. Round, where the breech may be as large as 1 1/8" across the flats, and are built to withstand the kind of pressure heavy loads, needed for long range shooting, can produce in the barrel.
My old Hodgdon Reloading Manual #39, lists RB loads For the gun topping at 70 grains of FFg powder and 1054 Fps. MV. SUBSEQUENT data from members here indicate that IN STRONGER BARRELS, you can use loads up to 110 grains . I HAVE SINCE SEEN MUCH HEAVIER CHARGES used in strong, Octagon Barreled rifles for hunting big game in Africa.
But these guns are not the Zuave Replicas sold by firms back in the 1950s and 1960s. Compared to the heavier barreled guns, the Zuave is rather light weight, and the recoil of even the 70 grains loads can be rough to take, simply because of the shape of the stock, and the steel buttplate.
So, before looking to change the sights to make this a " Long range " shooter, shoot the gun some with the existing sights and loads and find out what it can and cannot do. Any gun can lob balls or bullets onto distant targets, but doing so with any kind of consistent accuracy is expecting a lot.
The Zuave was used shooting a minie Ball- a short, hollow based bullet weighing between 315 grains, and 570 grains, depending on the length of the bullet chosen. That is substantially more than the weight of the .58 cal. Round Ball- at between 260 and 280 grains, depending on size chosen for a given gun's bore diameter.
I have watched competent match shooters shoot these guns out to 100 yds. I have watched Stake cutting shoots, where teams of riflemen competed to see which team could cut down a 2 x 10" plank using those minie balls, the fastest. The stakes were placed at about 50 feet for this competition, so that the audience behind the shooters had some chance of seeing the hits. I have followed the advice given hear, and elsewhere about using a Bullet sizing die to size the minie ball to within .001" of the bored diameter of the gun for best accuracy, and why to reduce the diameter of the plug for the casting mold so that you get a wider "skirt" on the hollow base, and a resulting heavier minie ball, so that heavier loads can be shot, without blowing out the skirt. The typical powder charge used for live fire shooting by re-enactors is 60 grains of FFg Goex Black powder. That is a pretty light load for that caliber. You can put a minie ball on a man sized silhouette target out at 100 yds, with it, but the drop in trajectory makes doing the same thing at 200 yds, much more difficult.
I don't have any experience with these guns being used for target shooting out at 300 yds, either witnessing it, or hearing about it. I therefore won't speculate about how its done, if its done, and if so, what kind of loads are used. Historically, the original rifles were not expected to be used to shoot at the enemy at 300 yds. or further.
Historically, The 1863 Springfield in .58 was a stronger-built rifle, and could handle heavier charges, than the Zuave.
