In 1938, Colt introduced a .22 LR caliber conversion unit to convert the Colt Government Model .45 and military variations of the same gun to .22 LR.  This unit utilized a patented "floating chamber" to simulate the recoil of a .45 that was designed by David "Carbine" Williams.  A big selling point was that the shooter could use this unit for target practice and the cost was approximately 1/7th that of target practice with .45 caliber ammunition.

In 1939, the retail cost of this unit was $34.00.  The small walnut display case for the conversion unit was available for an additional $3.50 and the large walnut box for holding both the .22-.45 conversion unit and wither the Government Model or National Match was $7.50.