It would be interesting to see a statistic of "gun owners" who impulsively commit suicide and suicidal people who plan things out and go buy a gun for the deed.
Would be nearly impossible to generate the info. A few years ago there was a local guy who committed suicide. It turned out he had one or more life insurance policies that had just lapsed the one year suicide exclusion. Not only that, but the normal is two years. The guy had started quoting insurance, asking for full copies of the policies, then studying the suicide exclusions months before he purchased to find companies with the shortest suicide exclusion. This wasn't a case of being out of work and looking for money to support his family either.
He did not use a firearm to commit suicide, but I don't see how you could stop someone with that level of resolve and planning to kill themself.