INQUIRER SENIOR WRITER One-gun-a-month laws sound attractive to gun-control activists and draw broad public support in polls. But it's not clear that such statutes have had much impact on gun violence. A study published last year in the journal Injury Prevention found that the laws restricting purchases had had no measurable impact. The study was done by a team of doctors from the University of Washington, using data from 1979 to 1998. Another study, done in 2001 by the Johns Hopkins Center for Gun Policy and Research, found evidence of a slight decrease in gun violence associated with Maryland's one-gun...