S&W M4 have mid-lenght gas system?

[armaliter]

Just a little confused over what is considered a "Middy" Most say anything that has a 9" gas tube which is what Ive measured on my M4 is considered that. The longer the gas tube the less pressure on the chamber. Where as a gas tube 7" is not considered a "middy". Do you measure from the hole in the FSB to the end of the tube in the chamber?

 

[jsimmons]

A mid-length gas system is dependent on where the gas port is located on the barrel, and that dictates the length of the gas tube. Since the hole is closer to the muzzle that a carbine-length system, yes, the gas tube has to be longer so it can operate the BCG (as it happens, about two inches longer).

I haven't seen a S&W "middie", but that doesn't mean it's not available.