#mp320

The Other SIG 320

Many of us will be familiar with the SIG Sauer P320 polymer framed, striker-fired pistol, recently adopted by the US military as the M17. What we may not have known, however, is that the P320 isn’t the only ‘320′ to have been developed by SIG. In the early 1970s SIG developed a futuristic looking new submachine gun - the MP320. 

The MP320 was apparently the last submachine gun developed by SIG Neuhausen as a successor to the utilitarian MP310. Dispensing with the folding magazine housing that characterised SIG’s line of submachine guns the new MP320 had a futuristic profile with svelte side-folding stock and a top-mounted charging piece which removed the need for a protruding charging handle and reduced snag points and with no large charging handle slot it also limited the ingress of dirt into the action. 

In terms of disassembly it appears that unlike the earlier MP310, the MP320 has a barrel bushing which unscrews and allows the action to be removed through the front of the weapon rather than the rear. It’s unclear if any of the upper receiver lifts out of the lower.

The rear peep sight is enclosed in a protective stamped housing while the low profile front sight is positioned just in front of the knurled barrel nut. The weapon appears to make extensive use of stamped, rather than machined, parts with the visible parts of the upper receiver appearing to be largely stamped.

SIG MP310 (source)

The weapon had a large rotating selector switch on the left side of the receiver, just above the pistol grip with positions for safe, semi, three-round burst and fully automatic. While the MP320 abandoned the classic SIG folding magazine feature it retained the same double stack, double feed magazine which had been used right back to the MKMS developed in the 1930s. The magazine relieve can be seen at the rear of the magazine housing.

It is unclear what the weapon’s rate of fire would have been although its predecessor, the MP310, had a high rate of fire of around 900-1,000 rounds per minute. It is also unclear if, like its predecessor, the MP320 uses a standard blowback action - but this seems likely.  

I came across it while reading the Vickers Guide SIG Sauer Vol.1 and this appears to be the only current source of information on this interesting submachine gun. The book notes that the gun never went into production and development was abandoned after only a handful of prototypes were produced.

Sources:

Vickers Guide: SIG Sauer, Vol.1, (source)

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