The initials stand for Board of Ordnance & Fortifications.

Some experimental Krag rifles were built in 1902 with barrels shortened to 26 inches, new made short stocks, and 1901 style rear sights with unique range graduations. These short rifles were fitted with bayonets.

IIRC - The "BoOF" rifles performed very well, but, the idea came too late. Prototypes of the 1903 Springfield were already underway.

Around 100 BoOF rifles were made and very few survive. Bits and pieces of them, may be around, hiding in plain view.

Dick Hosmer is very astute and knowledgeable on this rare Krag variant.