The first, obvious conclusion from FBI data is that a group making up approximately 4% of the US population commits about half the US homicides, mostly against others in that group, and the other 96% of the US has a homicide rate lower than England - and also much lower violent crime rate than England.
You would need to do the same segmentation of the English population, and compare like segments.
Any time someone purchases a gun from a store, or from most dealers at gun-shows, a background check gets run. This, + paperwork and records residing with individual sellers are your only real sources of data, neither of which are public.
The concept of a national gun registry has been debated hotly for quite a while, but that would definitely not be public if it existed.
(X = Reichstag Fire, Y = of potential communists, Z = communist party affiliation) (X = 9/11 Attacks, Y = of terrorists, Z = mosque attendance)
I guess you could, but has history taught us nothing? If I am a communist, am I a threat to you? If I am a muslim, am I a threat to you? If I have a gun, am I a threat to you?
I don't own a gun or have a gun license, nor do I want to be the victim of gun violence (or violence of any kind, having experienced it), but I don't know what you would gain from this information if you are looking to profile a potential disaster.
I think building a model on other factors about the people that commit these acts would perhaps yield better results.
[1] http://www.huffingtonpost.com/2012/12/19/mass-shooting-psych...
[2] http://www.livescience.com/21787-predicting-mass-shootings.h...
[3] http://andrewgelman.com/2016/02/25/probability-paradox-kills...
[4] https://bayesianbiologist.com/2013/06/06/how-likely-is-the-n...
Also check the Federal government statistics as organized by the US gun industry lobby, the National Shooting Sports Federation: http://nssf.com/ Look up the ammo production and importation numbers, well over 12 billion per year, and I'm not sure which include the seconds from the DoD Lake City plant that ATK sells to us (the Pitman-Robinson point of sale tax data will).
Maybe also check the raw numbers of concealed carry licenses, the GAO publishes these, but 10 states now don't require a license. I'll add that at the local level of my home county, Jasper in Missouri, as of a year and a half ago, 5% of the age eligible population had a $$$ Missouri concealed carry license ("$$$" because our's is one of the most expensive, and any state's will do if you want to save money). All these numbers are rapidly increasing as the population ages, as well as the other obvious reasons.
ATF Listing of Federal Firearms Licensees (FFLs) - 2016 https://www.atf.gov/firearms/listing-federal-firearms-licens...
This might offer a start.
You might find some of the data sources listed valuable.