"What difference does it make if 70 - 80% are suicides? An easily available gun makes suicide much more likely, and much more likely to be effective."

That is demonstrably false.  In Canada, for example, with successive gun control legislation (safe storage, licensing etc) we did see a reduction in suicide by firearm.  But we did not see a reduction in suicide.  Most males in Canada kill themselves by hanging.  Hanging is only 1% less effective than shooting oneself.  Other countries (i.e. Japan) that have very few civilian owned firearms have high suicide rates.  Method is irrelevant to the overall rate.