Samuel McClean’s Semi-Automatic Pistol

Perhaps best know for designing what would become the Lewis Gun, Samuel McClean was a talented inventor with over thirty, predominantly gun related, patents to his name by 1920.  

In 1898, at the age of 41, he patented an extremely complicated pistol which used a gas-operated, rotating locked breech action. His patent explains the basics of his invention: 

“[the pistol] consists of a gun-barrel and a receiver provided with a breech-block which has a reciprocatory movement from and toward the barrel to open and close the breech and a turning or rotary movement to lock it into engagement with or unlock it from the breech, combined with an automatic power device which upon each discharge of the weapon imparts said movements to the breech mechanism. Preferably said automatic power device is actuated by the force of the explosion of each cartridge and may be (and in the particular expression of the inventive idea herein shown is) actuated by the gases of discharge.”

Gases appear to be tapped off at the muzzle through a valve into a gas chamber which pushed the slide back and compressed a spring to push the slide and breech block rearward and unlocked the action. McClean explains further in his patent:

“a rotating and reciprocating breech-bolt, combined with a slide actuated by the gases of explosion, which slide is so connected to the breech bolt that upon each reciprocation of the slide the bolt is turned to unlock it, is then withdrawn from and returned to the breech, and is finally turned to again lock it to the breech.”

The barrel is surrounded by a main spring which resists the movement of the slide during operation. There is a small additional gas in the top of the barrel, just behind the front sight that acts as a “flange B to operate as a gas-check and an air-cushion and to permit the action of the primary actuating-spring F.”

The pistol feeds from a magazine in the pistol grip, however it loads not from magazines or stripper clips like some of its contemporaries but from a pivoting magazine which swings out from the grip to be loaded. The patent drawings suggest an 7+1 capacity. The pistol patent also mentions a magazine cutoff to allow single loading. with a rotating cut off lever on the left side of the frame. 

Intriguingly, the pistol has what McClean refers to as an ‘auxiliary trigger’, located just behind the trigger guard, marked ‘P’. It appears to act as a grip safety and interacts with the sear. A small sliding tab inside the sliding trigger guard, marked ‘Y’ can be pushed back to actuate the auxiliary trigger to facilitate ‘automatic loading, but not automatic firing’.  

It seems that McClean’s design is not calibre or firearms specific, he frequently notes that the action could be adapted to suite calibre and layout saying that the “breech-bolt may have any desired form necessary to adapt it to any preferred form of breech-bolt-locking action.” 

McClean was predominantly interested in gas operated actions and focused much of his work on developing larger designs to utilise captured propellant gases. His pistol is perhaps  over complicated but when compared to other contemporary designs of the day it is not the most outlandish. John Browning had also experimented with gas operated designs, a year earlier in 1897, he patented a pistol which used a pivoting ‘gas lever’ actuated by gas leaving a vent in the barrel - Browning, however, never appears to have experimented with a gas expansion-driven pistol like McClean’s.  

Source:

‘Gas-Operated Firearm’, S.N. McClean, US Patent #735131, 20/01/1898, (source)

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