One can only be certain when a case is decided by SCOTUS, and so far, no law has attempted to ban the publication of manuals for firearms.
Jackson v. City of S.F., 746 F.3d 953 gives good reason to think that the court would find such a ban unconstitutional. There is an analogous line of thinking regarding ammunition regulations, where some municipalities took the position that ammunition is not "arms" and therefore is not protected, since the amendment does not explicitly say "and ammunition". The Jackson court comments that
A regulation eliminating a person's ability to obtain or use
ammunition could thereby make it impossible to use firearms for their
referring to Heller, and SCOTUS's finding that
the Second Amendment protects an individual’s right to
possess firearms and that the city’s total ban on handguns, as
well as its requirement that firearms in the home be kept
nonfunctional even when necessary for self-defense, violated that right.
The Jackson court
conclude[s] that prohibitions on the sale of ammunition do not fall
outside “the historical understanding of the scope of the [Second
The reasoning that brings ammunition within the scope of Second Amendment protection applies equally well to e.g. ammo cases, gun oil, cleaning brushes, and instruction manuals, all of which are necessary to the lawful exercise of one's Second Amendment rights. See also Ezell v. Chicago, 651 F.3d 684 which holds that
the right to possess firearms "implies a corresponding right to
acquire and maintain proficiency in their use"
and thus a ban on firing ranges violates the Second Amendment.