Here's a little free advice from a Bachelor of History....
Gunfacts is a good place to start, but don't cite it! As good as their research is, their presentation comes off as being biased and many teachers will view it as such. So, how do you get around it you ask? Simple, go to the source!
Once you have found a relevent study on GunFacts, copy down their list of sources, then go to the library and look them up. This will not only give you all the data that GunFacts used, but also the data that they omitted. It can also lead you to more info on the subject (studies by the same author/agency).
Researching in this way is also very useful for debunking biased studies. A study may be published in a non-biased publication, but it could data from biased sources (or even partial data that skews the results). This type of research will impress most undergraduate teachers, and is expected in senior-level classes.