Produced by gunsmith Charles Kelsey, the Devel "Full House" package was a conversion of the Smith & Wesson Model 39 or Model 59 pistol (the 39 was a single stack and the 59 a double stack). In the late 1970s, there were really no factory-made semiauto compact pistols made for concealed carry - that was the realm of snubnosed revolvers. To meet the demand from the small group of sneaky and serious people, gunsmiths like Kelsey and Paris Theodore began to customize the available options - mostly S&Ws and Spanish automatics.

The Full House Devel conversion here included shortening both the barrel/slide and grip of a Smith & Wesson, shortening magazines to match (and in doing so reducing the Model 59's capacity from 14 to 10), bobbing the hammer, replacing the sights, adding a finger hook to the trigger guard, adding grip panels with a transparent window, and performing a plethora of minor adjustments to improve the reliability of the gun.

Only a few hundred of these conversions were made by Kelsey, as it was a very expensive option. They were prized in their day, and are directly responsible for the introduction of similar features as factory models from S&W and other companies. They look clunky and large by today's standards, but that is only because of the 30+ years of development that they spurred.