Here's the French appraisal of the "true" Nessler ball, i.e. with a rear cavity, vs. the solid collapsing skirt version of the North Carolina so-called "Nesler":
J. Corréard, ed.
Journal des armes spéciales et de l’etat-major (Paris: Librairie Militaire, Maritime et Polytechnique, 1866), pp. 271-73:
Model 1857 (rifle musket) Minié 32 gram/ 493-grain bullet backed by 4grams powder (approximately 60 grains, like the U.S. service charge). This rifle musket caliber measured 17.8mm/.71 caliber, a bit like the British Crimean War-era Pattern 1851 .702-in. rifle musket, which immediately preceded issue of the smaller caliber .577-in. Pattern 1853 Enfield.
1. Smooth bore (i.e. Mle. 1842 .70): Spherical 16.7mm/ .66 caliber lead ball, weight 27gram/ 415gr., powder charge 9grams/ 1/3rd of an ounce, or about 140 grains (U.S. flintlock muskets employed a charge of 120grains of coarse musket powder, part of which was used to prime the pan. Adoption of the percussion ignition system led to a reduction of the charge to 110grains).
2. Nessler conical ball for smooth bore arms, 16.7mm/ .66 caliber bullet weighing 30grams/ 464grains propelled by a 6gram/ 90grain powder charge. [Perhaps the charge for the North Carolina “Nesler” was similar, e.g. 100 grains, give or take, or perhaps it was reduced to 60 or 65 grains like the rifle musket charge? Certainly the compression on firing would seal the internal windage of the bore, increase the velocity, and scrape away some of the fouling?)Compared to the spherical ball of the infantry musket, that designed by M. Nessler for smooth bore arms displayed great superiority; see table below:
https://archive.org/details/journaldesarmes12unkngoog
All shots taken with Voltigeur Mle. 1842 (e.g. 4ft. 8-in. long, 9lbs. 9oz., 17.8mm/.70 caliber)
At 200 meters, shooting at a 2m x 1m target, spherical ball scored 35% hits, while the original French Nessler scored 60% hits. The Model 1857 minnie was reportedly 78.33% at that range.
Another 100 meters out, using the same target, the spherical ball had 25% hits, while the Nessler (the one with the hollow base) was at 43.33% hits, and the minnie at 63.33%. At 400 meters, and a bigger target, 2m x 2m square,no record at all for the spherical ball, and 38.33% for the Nessler ball. The source lists 43.33% hits for the minnie at this range, but I think this is mistaken, and is an error where the number for the Nessler from the preceding column was that number. At 500 meters the minnie was still 51.67% and all the way out to 550m on a 2m x 3m target, the French test concluded 40% for the minnie.
3. Mle. 1854 Imperial Guard rifle musket—17.8mm/.70 cal. (1.42m/4ft. 7-in. long, with a 1.03m/3ft 4-1/2-in. barrel rifled with four progressive-depth grooves, typically loaded with 4.5grams/69 grains of powder backing a skirted 36gram/554-grain Minié ball).
I've got some lead and I'm ready to start casting some of the replica "Type II" NC state so-called "Neslers" I'll have to try different powder charges. My understanding is that the service charge for the .69 cal. conical bullet was 70 grains of powder, while the undersized .65 cal. spherical ball used 110 grains.