Sinew vs Nylon bow strings. A Brief.

 The nylon string will always outperform a natural material string. They are faster on the bow, giving a sinew-backed bow a beautiful snap—because the material is by weight far stronger and lighter. 

The nylon string also has the important advantage of being impervious to weather. Though this matters little, as a sinew-backed bow it's used on can't handle water. They wouldn't be chewed by predators like sinew. 

However, where will you find nylon in the woods when it breaks? Sinew is, in my opinion, the second-best bowstring material, though I don't have enough experience making strings, as the ones I make don't often break. With a bit more experience, a string maker must find the sweetest spot between longevity and reliability and having a fast, thin sinew string.

The most important takeaway is the performance difference of the nylon string. A bow, which you may not want to hunt with, may become a hunting bow simply by switching from a sinew string to nylon. The effect on the arrow changing only from sinew to nylon is SIGNIFICANT.

Since it's up to me, however, I prefer materials that are only around 200 years old or later in my arsenal of archery equipment, so my nylon is a backup when no sinew is available or in the works. Practice in bowstring making is crucial.