All the 40K numbers were assigned in 1978. Your Model 19-4 could have shipped that year or the next.

Serial numbers for 1963-1968 ran from K515479 to about K848781. None of the K series serial numbers in that period had any digits before the letter.

In 1963, the Combat Magnum was still the Model 19-2. By 1968, it was a Model 19-3. The dash four did not come along until 1977.

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Jack
SWCA #2475, SWHF #318