I don’t know if Henry would use a different power hammer spring on a 357 rifle than something like a 243 or 308 ? I know the early guns had a 8 - 9 lb. trigger pull and most owners were changing out the hammer springs to lighten the trigger pull. I have heard that Henry was doing trigger jobs for those who complained and sent their rifles back for warranty work. The exploded view of the 015 rifle shows a double hammer spring like a spring in the center of another larger spring but you need to remove the stock to get at it and I have no idea what my gun has but it does have a fairly light trigger pull.
You may be right that between some excess headspace and a lighter hammer blow may be the problem.
Jedman