My older Navy Arms branded Zouave is really nice quality. I've had about 3 Zouaves, and all had musket nipples. Yes, dave951, Lodgewood is best for military generally.
Art, what thread is on the nipple for your Navy Arms Zouave? That information would help out the OP.
Also, I would respectfully suggest to the OP that he get a replacement nipple sized for musket caps. I believe these may be a bit hotter than #11 caps, they seem to be easier to get right now, and they would be more authentic for this rifle.
One other thing to consider is that most of the original 19th century guns had a bolster for the nipple welded or brazed to the side of the barrel, with a very simple, “flint” style breechplug. The flash channel was short and went directly to the main powder charge. Many of the early Italian reproductions, on the other hand, were made with a patent breech, in which the bolster, breechplug, and tang were cast as a unit, with a reduced-diameter chamber or “powder well”. A relatively longer flash channel leads to the bottom of the chamber, which leads to the main powder charge. My Navy Arms 1863 Springfield is made this way, as was a circa 1970’s Armi Jeager Zouave which passed through my shop last year. My point being that there may be some advantage in using a hotter cap to ensure ignition. It may be worth noting that the Armi Jeager Zouave came into my hands because the owner couldn’t get it to “go off,” and it was my job to unload it. This took about 90 seconds and a ball-puller, and I found he had loaded the rifle with two fifty-grain Pyrodex pellets. It was probably a good thing that the gun didn’t “go off” with that load, really, because I found the flash hole in the nipple had been bored out to about .080”. The rifle had evidently been owned and used by a reenactor for shooting blanks. I expect the new owner would have experienced some flash from the nipple, if that hundred grain load had lit up, under the heavy, conical bullet.
Anyway, if the OP’s Navy Arms Zouave were mine, I would verify the thread size and get a new nipple sized for musket caps, and I would shoot black powder rather than a substitute.
Just one old fool’s opinion, for what it’s worth.
Notchy Bob