In addition to singling out inadequate training, a report issued by the department's inspector general faulted deputies for violating basic firearm safety rules and making mistakes when using a new light attached to the gun, the Smith & Wesson M&P 9mm.
The weapon lacks a safety lever and requires less pressure to pull the trigger than the previous department-issued handgun, the Beretta 92F.
In 2014, the second year after the new handgun began replacing the Berettas among sworn deputies, the department saw 19 accidental gunshots in the field, a 500% increase compared with 2012, the report said.
A Times story published in June highlighted the increase in accidental gunshots by deputies since the adoption of the new handgun.
The inspector general found that the department's eight-hour training course for deputies issued the Smith & Wesson firearm was "insufficient to overcome old habits" learned from using the Beretta.
The report said sheriff's officials should consider at least doubling the hours of training and conducting internal affairs investigations into each accidental discharge.
"There is a continued risk that either [sheriff's] employees or civilians may be seriously wounded or killed by an unintended discharge," the 59-page report concluded.
A few deputies have been wounded in accidental shootings since the new firearm was introduced. No bystanders or suspects have been injured.
So far in 2015, there have been seven accidental gunshots by deputies working in the field, compared with nine in 2013. The department saw only three accidental discharges in 2012, the report said.
The report said the Sheriff's Department lacked clear policies for evaluating and testing equipment. The Smith & Wesson M&P was purchased without a competitive bid, the inspector general said.
The report also questioned the selection of a light that is mounted on the firearm. Sheriff's officials, the report said, have recommended that deputies use a switch on the gun's handle to activate the light, but some deputies have mistakenly pulled the trigger when they intended to turn the light on.
The Sheriff's Department began training new recruits with the Smith & Wesson firearm in 2011 and allowed sworn deputies to choose whether to swap their existing handgun for the M&P. Those who chose the new weapon had to go through the department's training program.
The Smith & Wesson handgun was chosen because it has an adjustable grip and needs the same level of pressure for successive gunshots -- a feature that sheriff's officials decided would improve shooting accuracy among recruits, especially women, the report said.
The heavier Beretta has a larger grip, requires about 12 pounds of pressure on the trigger for the first shot and four pounds of pressure for every shot thereafter.
The inspector general credited the Sheriff's Department for trying to solve the problem by requiring deputies to pass additional marksmanship tests.
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