Hamilton khaki Field mechanical h50 movement ETA07.701

I have a Hamilton Khaki Field Mechanical with the H-50 (ETA C07.701) movement and I’m trying to diagnose what failed in the barrel/mainspring assembly.

The watch first started running extremely inaccurately — around 30 minutes off per day — but at that time it still wound normally and I could feel a firm stopping point at full wind.

Now the issue has progressed:

• the crown can be wound almost endlessly,
• there is no longer any solid resistance at the end of winding,
• and…

Hamilton khaki Field mechanical h50 movement ETA07.701