ALK8944- thanks for the updated information. My info was applicable to much earlier production..and from a source I thought trustworthy. It may well be that by 1974 product mix/demand had made single alloys/heat treat a production necessity.

In them thar days I'd seen one model 15 that'd been "magnumized" and was markedly unimpressed. Thinking back on it, I'm not sure if the result was due to workmanship, materials or handloading.