The Second Edition of "The Krag Rifle Story" has additional details (Mallory, page 196) on Sub-Target Gun Company's device.  The bronze 'fixture' that attaches to the right side of the rifle seems consistent with the stock inletting on 'tbergdall's' Krag.

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Bingo, right down to the little arm on the cocking piece - which apparently is to extend to the left).

The only anomaly seems to be the placement of the rear mounting lug viv-a-vis the rear sight - of course it is a different model (1902) but it still shouldn't be that far off, unless the drawing is intended to be somewhat schematic as opposed to a perfect scale rendition.

Dick:  Rear part (sight notch) of 1902 sight extends a lot further to rear than 1901 sight.  (Only 5/16" short of rear rivet of hand-guard).  I don't think there is much of an anomaly.

It certainly does, of course. I'd never actually measured, though.

You are probably right, as everything else seems to work.

This is really quite an intricate device.  The bronze 'fixture' or armature, that attaches to the rifle, has pivots on its ends that link it to the machine.  The cylinder, which holds and marks the miniature targets, apparently lies on the machine 'bed' and is actuated by a cable.  (I've since learned, on some machines, the release of the trigger completes an electric circuit.  There is a dry battery located in the machine's pedestal.  An electro-magnet propels the sub-target into a pointed rod to be pierced, thus recording the 'shot'.  This is reported in the 1906 Wilkinson brochure).

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This is really very interesting.  What did the trainee aim at?  A target on the wall?  All this is before electricity, let alone any sort of electronics.  Simply setting up the machine must have been time consuming.  I assume that once set up, in a basement armory (gas lights), that the installation was more or less permanent.  Have any of these devices survived?  Any of the instruction manuals?  Or miniature targets?

All this makes me ask if there is a Krag museum anywhere?  tbergdall's rifle belongs in it, as does the carbine with New York letters burned into the stock.  I say Krag museum, because none of this would ever be shown in a museum dedicated to public schools.

I suspect the 'hay day' of the sub-target rifle machine was 1907-1908.  By 1908, the Public School Athletic League of N.Y.C. had put one in each High School, (reported variously as 11 or 12).
  Denise Conni, (N.R.A. Marksmanship Qualification Program Coordinator), in "100 and Counting" reports on early PSAL-NYC activities and competition with .22 Rifles and the ..."sub-target rifle machine -- a marksmanship training device with more than 300 parts and a lofty 1904 price tag of over $200..."
  I would guess over time the sub-target rifle machines required maintenance, adjustment, and repair.  'Virtual Shooting' and one machine per high school probably lost out to the economy and match environment with .22 target rifles.
  Possibly, 'tbergdall's' Krag, converted to .22 rim fire, is testimony to what happened:  An expensive training device probably lost out to target rifles that were practical, fun and inexpensive to shoot indoors.

The time frame makes sense.  Military-style training & competition shooting with the 22 rimfire began in England in 1900 and in the US shortly thereafter.  Stevens-Pope conversion barrels for Krags were marketed from about 1901 to 1904 or later.  In 1904, Gen. Crozier, Chief of Ordnance, issued the order saying all Krags that had been converted with Stevens-Pope barrels to 22 rimfire had to be returned to original military condition.  In 1905, Springfield began working on what would become the GPR, first issued in 1907.

In late 1904, Winchester produced the first of the Winder Muskets, filling the market niche formerly held by Stevens-Pope and the converted Krags.  The 1904-1905 selling price was about $17.

The Sub-target rifle (or gun) machine was the invention of Mr. Henry Havelock Cummings of Boston, Mass.  I have yet to find any exact instruction on how the rifle was attached to the machine's fixture.  Descriptions of its use and the (N.Y.C.) Public School Athletic League shooting program, which was a big advocate, can be found and read on-line. (Google search:  1. The Public Schools Athletic League, Outing 1908.  2.  Official hand book Public Schools Athletic League, Spalding's, published 1908).
  Wilkinson Sword Co. built the Sub-target device under license and advertised it in their  brochure of 1906.  The best descriptions are provided in the British materials, viewable on-line:  Google - Sub-target rifle shooting training devices - Rifleman.org.uk and select Wilkinson.
  BTW, the Sub-target machine, as manufactured by Wilkinson, was part electrical and utilized a 'dry battery' in its pedestal.  (Photo - a score card/post card from 1908 "School Boy Rifle Shooting Tournament" under Capitol Rifle and Revolver Assoc. and N.R.A. of America.  Note pin holes in target that were made by sub-target machine). 

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I wish they'd have had one of these in the backroom of the service station instead of the pinball machines.  A quarter for ten shoots would have been money well spent!   :D