Originally Posted by JP@AK

First, you always have to remember that published serial number cutoffs are only approximations, they are never firm. Moreover, the K prefix numbers were used on more than one model.

With respect to the Combat Magnum, only one or two left the factory in 1955, and not until December of that year. The first one produced was serialized at K260003 and it was assembled on December 15, 1955. Combat Magnum number K260001 was completed in January, 1956 (note: it was assembled after serial number K260003). By April, 1956, only 100 examples had been made. So, there probably were at least several with serial numbers below K266xxx that didn't leave the factory until sometime in 1956. In any case, just about any Combat Magnum you find was shipped after the first of the year, 1956, not in 1955.