I will read this more in-depth after I wake up a little, however, I can tell my some of your numbers that your stats include suicides, while bad I would argue should not be counted in a murder rate with firearms. Yes the US has a higher violent death rate, those articles I posted last night were about Mass shooting as that was the conversation we were having. I will read the CDC report. however I believe we do not have a gun issue in America, we have a human issue.
But that isn't the point I was trying to make here. I was making a point about statistical sources. If you cherry pick statistics, you can find criteria that will fit almost any model you want. The author of the report you linked to, is a guy named John Lott. He is an economist, who is therefore incredibly well versed in the manipulation of statistics. My opinion of him is that he is also a biased reporter, who has a vested interest in the specific statistics he reports, since he has written several books that sell very very well into the Second Amendment crowd. He would lose his income if he didn't spin the numbers the way he does.
But If you're looking to learn the scope of mass shootings, then look at mass shootings, set a simple definition that does not exclude mass shootings. The accepted definition seems to be, "Firearm discharge involving the injury or death of 4 or more individuals". It's not an official definition, it's just that is the most often cited definition and it seems reasonable to me. If you go on to exclude cases where no other crime was committed, you exclude exactly the kind of thing you would want to look at - namely, how big is the problem? Why is that? Because what constitutes a crime varies from jurisdiction to jurisdiction. That makes it very hard to make a fair comparison. This is true even if you just look at the US and ignore the rest of the world. There are 51 Governments in the USA, (counting Federal) and what constitutes a crime in each, is different.