Earlier this year American Handgunner ran a story about Walter Perrine’s interesting Pirahha Pistol. The pistol’s operating mechanism (Patent #3861274. Issued Jan 2, 1975) bears a striking resemblance to the KRISS Vector submachine gun/carbine. The blowback-operated bolt is connected by a linkage to a mass that actuates downward in the pistol grip, deflecting some of the recoil in a downward direction. The KRISS has a similar system although the bolt is connected to a mass that sits forward of the pistol grip, rather than in it.
According to American Handgunner, between 1969 and 1975 just 23 Pirahha pistols were producued.
[ Many thanks to Rufus for emailing me the info. ]Related