In the picture of the Krag action set up for the Sub-Target Rifle Machine (STRM) posted by butlersrangers, there is what appears to be a lobe attached to the striker.  The lobe is on the port side of the rifle instead of the starboard as shown in the first set of photos.  There is a rod fastened (threaded?) to the lobe.

The entire striker with lobe in tbergdall's Krag may be a replacement, one which replaced the issue bolt when the rifle was to be used in the STRM, hence the difference in striker knob knurling.  The lobe could have been rotated from its original position during reassembly at any time in the last hundred years.  Perhaps that is why sometimes the rifle can be cocked by pulling on it and sometimes not.

There was more than one kind of training device that held a rifle at shoulder height.  All date from about the same time period, the late 1890s until just before WW1.  This striker assembly could be from another one. Selling gizmos to the Army would make you rich.