SIG MCX Virtus short stroke piston

[jski]

The short stroke piston used in SIG’s MCX Virtus rifle is the same SSP developed by “Carbine” Williams, correct?

 

[Tommygunn]

Similar in principle but a little more complex in design.

 

[jski]

Similar in principle but a little more complex in design.

When I heard it used the short stroke piston design from the AR18, I thought who other than “Carbine” Williams designed/invented a short stroke piston?

 

[zaitcev]

When I heard it used the short stroke piston design from the AR18, I thought who other than “Carbine” Williams designed/invented a short stroke piston?

Dieudonné Saive and Sergei Simonov did, as I'm sure many others. Saive patented what later became FN-49 in 1936. Simonov presented the first protype in 1931, the rifle accepted into service in 1936. Williams made his invention in 1940, or substantially later than either of the previous short-stroke gas-operated rifles. What he invented was different: he invented a gas tappet system.

In a conventional short-stroke design, the gas is vented after a certain amount of travel of the piston. Typically the point at which the gas is vented is regulated. FN-49 featured a fine adjustment, although most modern guns just have "normal" and "difficult" setting, and a cut-off for rifle grenades and the like. In addition, most designs, including early Simonov's and Saive's designs, have the whole op-rod moving the short distance and disconnecting from the BCG somewhere in the receiver.

In Williams' gas tappet, the short travel is limited mechanically and any venting is incidental. In addition, in both W.A.R. and the M1 Carbine, the op-rod is attached to the bolt carrier. Williams thus avoided a need for the 2nd spring that returns the gas piston.

 

[jski]

Dieudonné Saive and Sergei Simonov did, as I'm sure many others. Saive patented what later became FN-49 in 1936. Simonov presented the first protype in 1931, the rifle accepted into service in 1936. Williams made his invention in 1940, or substantially later than either of the previous short-stroke gas-operated rifles. What he invented was different: he invented a gas tappet system.

In a conventional short-stroke design, the gas is vented after a certain amount of travel of the piston. Typically the point at which the gas is vented is regulated. FN-49 featured a fine adjustment, although most modern guns just have "normal" and "difficult" setting, and a cut-off for rifle grenades and the like. In addition, most designs, including early Simonov's and Saive's designs, have the whole op-rod moving the short distance and disconnecting from the BCG somewhere in the receiver.

In Williams' gas tappet, the short travel is limited mechanically and any venting is incidental. In addition, in both W.A.R. and the M1 Carbine, the op-rod is attached to the bolt carrier. Williams thus avoided a need for the 2nd spring that returns the gas piston.

Which does the AR180 and SIG VIRTUS use?
Williams’ or Simonov’s?

 

[zaitcev]

Which does the AR180 and SIG VIRTUS use?
Williams’ or Simonov’s?

The AR-18 used Simonov's cup, essentially unchanged. It's lineage is AVS-36 -> SVT-40 -> G.43 -> AR-18 -> Virtus. The core of Simonov's invention was the 3-part cup, which allows one to take the system apart without any screws or plugs. It's magic, really. That is why it was so widely copied in Germany and the U.S.. That said, Simonov himself switched to a generic piston in SKS, which works just like Savie's piston, only it's not even regulated, just over-gassed. It's mystery why.

It's also a bit of a mystery to me why Williams' tappet fell out of fashion. It was said to be difficult to clean, but surely it could solved with a plug in front. Even Russians use that plug in AK-12 these days.

 

[briansmithwins]

The FN F2000 and SCAR both use short stroke pistons with very limited travel and gas venting. They have the advantage of having adjustable gas regulators and are easily disassembled for cleaning.

BSW