Correct nock to string fit:

I would consider proper nock to string fit to be a commonly overlooked or ignored tuning or troubleshooting consideration.

Arrow nocks that are too tight-fitting or too loose-fitting on string WILL cause grouping and accuracy problems, more than some know or believe. Incorrect nock fit WILL affect the vertical and horizontal flight/impact, but the problem is too commonly believed to be the result of other more popular causes.

As your string wears or you install a new string, especially if the string has more or less strands than what was previously on the bow, you need to check your nock fit and readjust the fit as required.