Double Action Only Rationale

Hated by Jeff Cooper, loved by police liability lawyers, double action only (DAO) duty pistols are a breed all their own.
From the late 1890s on cops were trained to cock their service revolvers to light-pull SA on the range, and reserve DA shooting for emergencies. This lingered with some departments even as late as the third quarter 20th Century, though most figured out long before then almost any line of duty shooting was an emergency, and the emphasis had to be on DA.

About half a century ago, LAPD became the first major agency to render all service revolvers DAO, for two reasons. Under stress in gunpoint situations, it was easy to unintentionally fire a cocked revolver. Second, it left officer and department alike open to false allegations of negligence the hammer had been cocked even if it wasn’t. Miami PD, NYPD, Montreal, Canada Police and more followed with DAO revolvers.

DAO Autos

The ’70s and particularly the early ’80s saw the “high capacity nine” becoming the gun of choice among cocaine cowboys and gangbangers, and police unions sought firepower parity. Fearing cocked and locked guns, chiefs who adopted autos mostly limited them to traditional double actions, which self-cocked after the first shot and required a decocking lever to be hit when the shooting ended. Cops unaccustomed to these guns occasionally fired in the line of stressful duty and forgot to decock, creating a safety problem setting the stage for negligent discharges. The solution? The DAO semi-auto.

When in the late ’80s through early ’90s the two largest municipal police departments in the U.S. finally authorized semi-autos for their rank and file, both went DAO. Then and now, NYPD’s 36,000 officers have been limited to the S&W 5946, the SIG P226 DAO, and the GLOCK with super-heavy (12-lb.) NY-2 trigger. Chicago PD’s 13,000 sworn pistol packers were initially limited to DAO hammer-fired guns by Beretta, Ruger, SIG and S&W, with GLOCKs and other striker guns not authorized until considerably later.

Beretta, SIG and S&W were the main purveyors of police duty pistols, and they all saw the rapid ascent of their new arch-competitor GLOCK — in part due to ATF classifying the GLOCK as DAO. S&W designed the one with the best trigger — light, smooth and relatively short, but lacking second strike capability because the slide had to cycle to re-set the trigger.

The DAO Beretta, the D-series, had a long but lighter pull thanks to a lighter mainspring. It had second strike capability, that is, it gave a chance to light off a misfired cartridge without racking the slide. SIG took a similar approach with their DAO variation of the P226, followed by HK with their first such variant of the USP. Unfortunately, these latter had trigger pulls most found sub-optimal.

H&K and SIG got the message which led to hybrid, quasi-DAO service pistols.

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