U.S. Army manuals circa 1970s referred to both revolvers and M-1911 type handguns as pistols. All contemporary references I have seen during the 1860s referred to handguns such as Colt M-1851, Colt M-1860, Remington M-1858, various Confederate models, etc., all as pistols and sometimes unofficially "six-shooters". So, all handguns are pistols and some pistols are revolvers.
