What is the international evidence?

There is absolutely no evidence to even suggest that any gun control law restricting firearms passed anywhere in the world has produced a recordable decrease in in crime or the supply of firearms to criminals.

This is in direct accordance with other findings that there is no causal relationship between levels of firearm ownership and crime.  That means no matter what you do in restricting firearms it is impossible to decrease rates of crime.  It has many times been documented that gun control can and often does cause an increase of crime.  Case studies of Australia, Brazil, Canada,  Jamaica and the USA show the influence of gun control laws and for the USA the results after the removal of several gun control laws.

The Carter administrations appointed research of Wright, Rossie and Daley is a survey of felons and very telling of the criminal attitude and mind. The censored government report runs to three volumes. The investigators book has been published and contains most of the data.

Armed and Considered Dangerous: A Survey of Felons and Their Firearms (Social Institutions and Social Change)
Publisher: Aldine Transaction; Exp Sub edition (December 31, 1986) ISBN-10: 0202305430 ISBN-13: 978-0202305431

Review

Interviewing felony prisoners in ten state correctional systems in 1981, Wright and Rossi found extensive information suggesting that gun control laws have relatively little effect on violent criminals. For example, only 12% of criminals, and only 7% of the criminals specialising in handgun crime, had acquired their last crime handgun at a gun store. Of those, about a quarter had stolen the gun from a store; a large number of the rest, Wright and Rossi suggested, had probably procured the gun through a legal surrogate buyer, such as a girlfriend with a clean record.

Fifty-six percent of the prisoners said that a criminal would not attack a potential victim who was known to be armed. Seventy-four percent agreed with the statement that "One reason burglars avoid houses where people are at home is that they fear being shot during the crime." Thirty-nine percent of the felons had personally decided not to commit a crime because they thought the victim might have a gun, and eight percent said the experience had occurred "many times." Criminals in states with higher civilian gun ownership rates worried the most about armed victims. Despite the popular myth that criminals preferred small, inexpensive handguns (so-called "Saturday Night Specials" or "junk guns"), the felony prisoners preferred larger, more powerful handguns-equal to the guns which they expected the police would have. Although the criminals rarely bought guns in gun stores, the overwhelming majority stated that obtaining a gun after their release from prison would be a simple project, which might take a few hours to a few weeks.

Under the Gun: Weapons, Crime and Violence in America
By James D. Wright, Peter H. Rossi, Kathleen Daly
Published by Aldine Transaction, 1983 ISBN 0202303063, 9780202303062

Our gun control policies are being made in an information vacuum.

There is no persuasive evidence that: (1) there would be fewer homicides if firearms were less generally available, (2) gun ownership is per se an important cause of violence, (3) higher rates of homicide in the southern United States and certain other nations are due to higher rates of gun ownership, (4) private ownership of firearms is an important deterrent to crime, and (5) all other things being equal (for example, assailant Intent), gun assaults are more lethal than attacks with other weapons. Further, these writers dismiss the popular "fear and loathing" hypothesis that attributes most of the increase in firearms sales to fear of crime, minorities, and civil disorder.

That the more they explored the implications of the case for gun control, "the less plausible it became," and that there is more than a little truth to the oft-criticized aphorism that "when guns are outlawed, only outlaws will have guns." These social scientists see little hope for solving the problem of heat-of-passion homicide through firearms control laws, and suggest that we need to consider the broader and more fundamental problem of interpersonal hatred. They suggest that banning handguns could make things worse, rather than better.

Overall, the authors conclude that the prospect of ameliorating criminal violence through stricter civilian gun controls is dim.

Defensive gun use (DGU)

Klecks survey but there are more than twenty others who have all found a benefit to armed defence. The only argument is how good. 

Gary, Kleck and Marc Gertz, "Armed Resistance to Crime: The Prevalence and Nature of Self-Defense with a Gun," Journal of Criminal Law and Criminology 1995, Vol. 86 No. 1.)

How Often Are Firearms Used in Self-Defence?

There are approximately two million defensive gun uses (DGU's) per year by law abiding citizens. That was one of the findings in a national survey conducted by Gary Kleck, a Florida State University criminologist in 1993. Prior to Dr. Kleck's survey, thirteen other surveys indicated a range of between 800,000 to 2.5 million DGU's annually. However these surveys each had their flaws which prompted Dr. Kleck to conduct his own study specifically tailored to estimate the number of DGU's annually.

Subsequent to Kleck's study, the Department of Justice sponsored a survey in 1994 titled, Guns in America: National Survey on Private Ownership and Use of Firearms (text, PDF). Using a smaller sample size than Kleck's, this survey estimated 1.5 million DGU's annually.

John Lotts and David Mustard study of the USA over 18 years. 
More guns,less crime. The critics and Lott's answers See:

Youtube Video Interview
An interview with John R. Lott, Jr. author of More Guns, Less Crime: Understanding Crime and Gun Control Laws

The National Academy of Sciences
Firearms and Violence: A Critical Review (2004)
Committee on Law and Justice (CLAJ), Committee to Improve Research Information and Data on Firearms

-- There is no credible evidence that "right-to-carry" laws, which allow qualified adults to carry concealed handguns, either decrease or increase violent crime. To date, 34 states have enacted these laws.

-- There is almost no evidence that violence-prevention programs intended to steer children away from guns have had any effects on their behaviour, knowledge, or attitudes regarding firearms. More than 80 such programs exist.

-- Research has found associations between gun availability and suicide with guns, but it does not show whether such associations reveal genuine patterns of cause and effect.

Center for Disease Control (CDC)
First Reports Evaluating the Effectiveness of Strategies for Preventing Violence: Firearms Laws Findings from the Task Force on Community Preventive Services

The systematic review development team identified 51 studies that evaluated the effects of selected firearms laws on violence and met the inclusion criteria for this review. No study was excluded because of limitations in design or execution.   Information on violent outcomes was available in 48 studies, and the remaining three studies, which provided information on counts or proportions of regulated firearms used in crime, were used as supplementary evidence. Several studies examined more than one type of firearm law.

Evidence was insufficient to determine the effectiveness of any of these laws...

Cross country comparisons

The Samurai, the Mountie, and the Cowboy: Should America Adopt the Gun Controls of Other Democracies
Publisher: Prometheus Books (July 1992) ISBN-10: 0879757566 ISBN-13: 978-0879757564

The constitutional right to arms

That Every Man Be Armed: The Evolution of a Constitutional Right (Independent Studies in Political Economy) by Stephen P. Halbrook (Author) "The right of the citizen to keep arms has roots deep in history...
Publisher: Independent Institute (March 1, 1994) ISBN-10: 0945999380 ISBN-13: 978-0945999386

In SA, John Man (Published in The Citizen) and Magnum are the only two studies.

Altbeker and SAPS research (docket surveys) are not representative as dockets represent only reported crime.  It is impossible to thus estimate how many crimes are prevented or stopped if there is no injury or the SAPS are not called.  Due to the antagonistic and militant nature of the SAPS in the treatment of firearm owners few of those incidents will be reported or a firearm mentioned in a report for fear of losing a licence or being charged with a crime.