OK. I'd recommend heading over to the North-South Skirmish Association BB, they have all the expertise on the Minie ball. If nothing else, you might want to have the barrel freshened...that's smaller than any bore I've heard of.
Ok, I'm in the NSSA and compete regularly with muskets and minies. My competition musket is a repro of an 1862 Colt contract Springfield, bore dia is .580. And with the correct load, it will make one large hole at 50yds.
That said, many in our assoc use Zouaves, especially as starter muskets. That doesn't mean they can't be extremely accurate, just that they're fairly inexpensive. The issue with Zouaves is that they were made by a number of different shops and bores and quality can be all over the place. Most will shoot very well. There are only a couple brand repops that are total crap. I am currently involved in working up a number of Zouaves for a Boy Scout shooting program. All muskets measure at least .579 bore size. I have never heard of a Zouave under .575. Nearly all are "large" at about .578-9 and I've heard of some going up to .583.
I have several sizing suggestions- first be sure of the bore size. How? Get pin gauges. They're pretty cheap as you'll only need a couple sizes to find out. You could also take it to a local machine shop and have them check. Past that, go to Lodgewood (one of our supporting vendors) and look at the bullets page. You can order sample minies of various sizes for testing before buying a mold and sizer die.
Getting a mold- IF you are so fortunate as to have one of those Zouaves that truly takes a .575-7 minie, there are a couple cheapo Lee molds. My experience here, you get what you pay for. I have molds from Lee, NOE, Oldfoxtraders, Moose, Lyman, RCBS and Rapine. Depends on the gun as to which mold is in use. For muskets, my Parker Hale likes the RCBS Hogdon sized to .576 and is a sub 2moa gun. The Colt likes .580 Rapine "Trashcans". My Smith likes the Moose. My Sharps, Oldfox. Of my competition guns, only the Parker Hale will shoot anything from Lee, and that is the "competition minie" and that mold is sadly, not longer in production. NO other Lee bullet will shoot in ANY of my guns satisfactorily.
Now back to Zouaves. Because they're made by a number of different shops, the rifling twist rate can vary. There are some Zouaves that will absolutely not shoot any of the lighter minies. I have one in my possession at the moment for the Scout project that will not shoot anything lighter than 500gr. The others are fine with the RCBS Hogdon (375gr) sized to 579 and all of them will put 10 shots in a row into 2in at 50yds. They could probably be tighter, but for Scout use, 4moa is absolutley good enough, especially since we're talking 10 shots with no wiping or any form of bore maintenance between shots. That way, we can keep the muskets on the line with the boys for longer stretches.
A couple final comments, use ONLY pure lead for minies otherwise, the skirts will not reliably expand to grab the rifling. DON'T get caught up putting in more and more powder. Best accuracy is generally in the 60-75% range if the service charge of 60gr and yes, you can use 3f in a musket. Minie lube is an issue of extensive discussion with us, most use some form of beeswax/crisco/lard/oliveoil. Avoid Alox, it don't play nice with black powder.
Last of all, welcome to the addiction. Have fun with the Zouave. It can be a fine shooter when you get the combination right.
