Might that have been the ten smoothbore Winchester 70s used in 1959 by AAI to test the "Cartridge, .22" Caliber, Arrow", as part of the SPIW (Special Purpose Infantry Weapon programme), which fired a 10 grain, 0.72" saboted flechette? The idea being to create a very high cyclic rate, low recoil, small calibre infantry weapon that would give much higher hit probability than anything else known, but ended up being a colossal waste of money?