tokens: Most PDWs also use a proprietary cartridge , such as the 5.7×28mm cartridge for the FN P90 or the 4.6×30mm for the H & amp ; K MP7 , neither of which were originally compatible with any existing pistols or rifles ( although both manufacturers planned handguns that used the same proprietary rounds , only FN went forward with production of the Five-SeveN pistol , which is the only handgun option available for the 5.7×28mm cartridge for over two decades until the introduction of Ruger-57 in 2019 ) , which in turn made the PDW cartridges expensive to consumers due to the lack of mass production .