IMPORTANT INSTALLATION INFORMATION:
Nylgut is a completely different material than Nylon and needs a bit of extra care during installation because of its soft surface and different molecular structure.
First check that the string channels in the nut are rounded and have no sharp edges, especially the lower edges facing the fingerboard. Because the string approaches from a slightly downward angle, if that edge is sharp the string can hang up on it, create a burr and break. It needs to be just slightly radiused, and this procedure can be done with very fine sand paper and an old string, or a small round file. Some makers ignore this because Nylon strings are very hard and can withstand a poor set up. Sometimes bridge saddle edges on the tying side are sharp as well and should be radiused slightly with fine sandpaper.
It is good to help the strings over the nut by lifting them slightly right at the nut as you tune up. Plain Nylgut trebles stretch like crazy so you should also cinch the strings up tight on the barrels before winding. Be sure not to overlap wound strings on the tuning barrels. The preferred method is to put a set on an instrument in the evening, bring them just up to pitch, let them sit overnight, and finish tuning in the morning. This allows the molecules some time to adjust to being stretched. Give them a week or so to stretch in fully (less for ukulele strings) before passing any judgment on tone as it takes a while for them to develop their best sound.