This research compares states’ concealed carry handgun laws (may issue vs. shall issue), and explains the geographic and temporal patterns of the spread of gun control legislation across the country.

Findings:

Current handgun debate

• Proponents claim that criminals can migrate to neighboring jurisdictions with more restrictive concealed-carry rules. 
• Opponents claim that more guns lead more homicide and spontaneous violence. 

Shall issue vs. May issue

• Shall issue: the authorities do not have discretion to decide whether or not an applicant has a good reason for needing a permit and will normally be required to issue a permit unless there is some disqualifying factor (e.g., an applicant is a convicted felon)
• May issue: more restrictive than “shall issue” that may issue allows the issuing authority to require applicants to state a reason for needing to carry a concealed weapon.

Less urban states (Indiana, Maine, Georgia, Pennsylvania …) are more likely to shift to “shall issue,” and the decision to enact “shall issue” is influenced by the decisions taken by neighboring states. More urban states (California, Hawaii, Massachusetts, New Jersey, New York…) remained “may issue.”

Republicans are friendlier toward gun ownership than Democratics.

http://rgrossman.web.wesleyan.edu/Research/Grossman%20Lee%20May%20Issue%202008.pdf