The Cummings design was produced by the Sub-Target [sometimes “Subtarget”] Gun Company. These were actually used extensively by the U.S. Navy both at shore stations and aboard ships; the U.S. Army and National Guard; at both USNA Annapolis and USMA West Point; and also by a number of New York City Public Schools.
They were also used by a number of foreign nations, with the basic machinery being the same, the only difference being what service rifle was modified for attachment to the contraption.
Basically, they allowed decent training in sight picture and firing with the results showing on a miniature target attached to the bulky machine. It could be done without need for a firing range with attendant safety issues, but used a distance to the target aimed at of about 50 feet. They actually held match competition among the NYC public schools with teams competing at Madison Square Garden circa 1908-1916.
No ammunition was used, and the rifles were modified for attachment to the machine with dovetails cut on the underside of the barrel, and mechanical cables linking the striker to the needle device to poke the hole when the shot was fired. Mechanical linkage moved the needle up/down-left right to record the position relative to the distant target used for aiming.
The “Sub-Target” machines were sort of the ultimate absurdity of aiming practice which had begun circa 1850s with “candle practice” where a percussion cap on a standard infantry weapon would generate enough air movement from the barrel to blow out a candle a few feet from the muzzle. This was continued in the 1870s with “candle practice” primers and cases for .45-70 trapdoors. (See Dwight Jackson article in IAA Journal 482, Nov/Dec 1022)
Col. George Wingate’s “Indicator for Aiming Drill” was patented in 1876 and the first of the “needle” type marksmanship devices. Then came the Hollifield, and finally the Sub-Target devices.
The limitations of simplistic aiming drills was superseded by more actual gallery practice on indoor ranges, especially with national guard or cadet type groups. Sometimes with service rifles with special subcaliber cartridges. Other times, special variations of service rifles were made to use subcaliber ammunition, often .22 rimfire. Initially the U.S. used the Hoffer-Thompson design with cartridge holders to simulate .30-06 cartridges for loading drill purposes, then they switched to .22 caliber versions of the Krag and 1903 rifles chambered specifically for .22 rimfire.
I did an article in the Arms Heritage Magazine Volume 8 number 4, August 2018 going into U.S. military gallery practice arms and ammunition in considerable detail.