My guess is custom gunsmithing.
+1. FWIW the prewar fixed-sight .38/44 Heavy Duty has long been fodder for gunsmith conversions. Although these guns have become uncommon today, IIRC they actually remain S&W's all-time best-selling N frame model, and LE surplus examples were once available for a song. Consequently, in the 50s and 60s, they became fodder for a number of custom 'smithing projects by folks who could not afford a new Model 29 or whatever. (This phenomenon helps explain
why nice original .38/44s are uncommon today!) You'll still see the odd example pop up on a random gun show table.
BTW if a gun is in fact a .38/44 conversion, and the converted caliber starts with "4" and ends with "Magnum", I personally would not fire it unless the procedure involves a Ransom Rest, a 15'-long piece of string, and an earthen berm to cower behind.