However, it would be much better if someone could share the actual research with us.
As a PSA, don't ever try to kill yourself with a gun. The success rate is only 70 percent. The 30 percent who survive are much worse off than the rare jumper who survives the golden gate bridge
Is there something you can point to that supports that theory? I appreciate that you say you are "guessing".
Also, I don't know what "thinks about suicide for years" signifies. Probably everyone thinks about it at some point, and probably at multiple points; thus we all 'think about it for years'. I thought about being a fireman for years when I was a child. There's a big difference between thinking and acting, or there would be a lot more startups in the world.
This research comes from a few places: looking at people who've died by suicide and the methods they used, and any previous attempts. Looking at survivors of suicide attempts, and at what methods they've used in the past. And some natural experiments, such as the introduction of catalytic convertors to cars, or switching the UK gas supply from coal gas to natural gas.
A gun is brutally efficient at killing you; Load and pull the trigger. If the gun is lying around loaded, all you have to do is pick it up and pull. A gentle flick of the finger and it's over.
“I felt so guilty that I had put my family through such pain. I felt horrible.”