NRA rule 10.1.8 "BLANK"

Why was 10.1.8 left blank yet referenced in two other spots in the rulebook?

Have you checked prior versions of the Rules?  It sounds like it could be a holdover from a previous edition, i.e., the updated rules didn't catch all the instances 10.1.8.  Section 10.1.11 is missing altogether as well, but is referenced on one of the same pages as 10.1.8. (under Shooters Read).  In that same section, there is a reference to Loaded Firearms 10.1.3 but the actual section below is titled Loaded Pistols (not Firearms). No doubt there are other inconsistencies.

Updating rule books (or statutes or code sections or indices or ...) is tedious work that rarely goes smoothly. (Trust me, I know this full well.)

All of which is to say, it is probably an editorial oversight.  

In some cases the "blank" rules are those that do not apply to that particular discipline. (For example, that particular rule(s) would be specific to small bore rifle and not needed for precision pistol.) 

In other cases, its just editing not catching up with changes, etc.

CR