And is there a common underlying cause?
Availability of drugs or guns surely plays a role, but if you give the average person an AR-15 and a syringe of heroin, they're unlikely to use either. So there are more factors at play.
Russell Brand states in Recovery "Addiction starts with pain and ends with pain", it also cites a study that concludes that lab rats will choose social interaction over heroin or meth but in isolation they will overdose. I think it would be fair to say that violent crime also starts with pain and ends with pain. So besides guns, there are other underlying factors that need to be addressed.
Link: https://healthpolicy.usc.edu/article/american-drug-overdose-death-rates-the-highest-among-wealthy-nations/