The only logical conclusion I can draw from your post is that, proportionately speaking, we therefore must have the most amount of sociopaths of all the 1st world countries?
Because if it isn't guns killing people, then they would be homemade bombs and trucks. Like that happens in the UK, Switzerland, Finland, Norway, etc. ??
But in America, that doesn't happen. Some of the worse driving into a crowd incidents here were old person driving or drunk-type. Not premeditated murder. (And yes, there have been a couple cases of that). But by and large, mass deaths in this country continue to be via gun. Not bomb, not truck, not car, and not knife.
Because 1st world European countries have a stricter gun policy, but presumably a similar number of proportionate pyscho/nutjobs, you would think you' see more cars ramming into people or bombs going off. But that's not happening. Those in Europe are almost exclusively reserved for terrorists.
So no, the argument of "if not guns, then bombs or cars/trucks" doesn't really bear truth based on the evidence of other countries.