Despite efforts to address the problem, the risk associated with the new Smith & Wesson M&P 9mm "remains substantial," according to the report by Los Angeles County Inspector General Max Huntsman.
"There is a continued risk that either LASD employees or civilians may be seriously wounded or killed by an unintended discharge," Huntsman wrote.
He said further study and steps to mitigate the problem are needed "before a tragedy occurs."
A handful of deputies have been injured in accidental shootings in recent years, according to the report. No suspects or bystanders have been hurt in the incidents.
The report, an advance copy of which was obtained by CNN, found that a sheriff's department training program for deputies converting to the new gun is inadequate.
"We conclude that the current training program is insufficient to overcome old habits learned on other handguns," the 52-page report states. "As a result, many deputies appear to be to undertrained for the weapon they are using."
Assistant Sheriff Todd Rogers, a top aide to Sheriff Jim McDonnell, said in an interview Wednesday that department officials had noted the trend with accidental discharges associated with the gun prior to the IG's report and independently took steps to address the problem.
"We welcome the IG's input as to some things we can do better," Rogers said, "but we saw this coming before any outside pressure caused us to respond."
Rogers noted that accidents were down so far this year, which he attributed to the department's efforts to mitigate the problem.
The department went to the new gun, in part, because it is easier to handle and easier to shoot accurately, particularly for people with small hands. The gun comes with a smaller grip and requires significantly less pressure to pull the trigger than the Beretta 9mm that had been standard issue in the sheriff's department for years.
The LASD began issuing the Smith & Wesson to all new recruits going through the academy beginning in 2013. Veteran deputies were allowed to transition to the gun if they took an eight-hour training course. The department has since issued about 6,100 of the handguns to its deputies.
The IG found that "as soon as widespread use of the new gun by field deputies commenced, there was a marked increase in tactical unintended discharges -- that is, deputies firing weapons without intending to do so during police operations."
In 2014, "after substantial adoption of the new weapon in patrol settings," the report noted, accidental discharges in the field shot up by more than 500% -- from three in 2012 to 19.
Sixteen of the accidents involved deputies armed with handguns, the report found. Fifteen of those were carrying the Smith & Wesson.
So far in 2015, LASD deputies have been involved in 18 such shootings; 14 involved the Smith & Wesson, according to the report.
That figure is down from the dramatic increase in 2014, but still represents a 61% rise from the year before the gun was introduced, Huntsman's report states.
The IG's review found several factors that "apparently contributed" to accidents with the gun since its introduction:
--The weapon lacks an external safety;
--It's more sensitive than the Beretta;
--And a light mounted to the gun and activated by deputies squeezing a pressure switch on the handle has led to confusion in some incidents, with "a significant number of deputies reporting that they unintentionally pulled the trigger of their weapon when they intended only to turn on the light."
Adding to the problem was some deputies violating a basic firearms safety rule by placing their finger on the trigger prior to making the conscious decision to fire, the report states.
The IG recommended the sheriff beef up the department's training program for deputies converting to the gun beyond the eight hours currently given, noting that "few agencies consider that amount sufficient."
The IG also recommended an "in-depth" analysis to determine whether the pressure grip light switch was warranted.