GSh-4MS, Soviet Test-Pilot Flight Helmet
Hermetically Sealed for High-Altitude Flights

 Here is a GSh-4MS.  This is a helmet for test pilots that was designed in the 1950's and used to the late 1960's.  This helmet is dated 1967.

The difference between this helmet and the GSh-6 is that the -6 came later and was used by both your average pilot and test pilots.  Finally in the late 1990's, test pilots switched to the ZSh-9 (the aircraft currently being tested is the Multi-Function Fighter being built by Sukhoi.

The helmet does not have integrated communications, but it does have a separate helmet made of fire-resistant material.  It has a boom microphone with integrated earphones.  You'll readily see this as the predecessor to the GSh-6's communications helmet.  The headphones are covered with soft lambskin. You'll note that on this one, the string adjuster for the top of the helmet is missing.  You'll also note that the helmet ties in place - no buckles of any kind.

The communications plug hangs out the back of the helmet and plugs into the aircraft communications suite.

This view shows how the plugs and wires come out the back of the helmet.  The neck skirt is long, draping down to the pilot's shoulders.

These helmets were only made in sizes 1 and 2.  In order to get the best information and for designers to have the most flexibility, Soviet test pilots were not large men.  

Also note that the visor is electrically heated.  If you have the Jet Age Flight Helmet book, then you will see other differences between this helmet and the one in the book.  This helmet does not have the dark visor.  You can see that it doesn't have the fittings for the dark visor either.  Each GSh-4 was unique and this demonstrates it.  

Here's a view of the inside of the helmet.  The adjustment strings are on the neck skirt and there is a leather net on the inside so the pilot's head does not bounce off the metal plate.  You can also see that there is no insulation in this helmet.  It is a thin layer of metal that I believe is aluminum.  There is no rust, although there is a little exposed metal along the edge. 
Here's the tag for GSh-4MS serial number 671284.  The size is indeed a 2 (not 1 - although it does kind of look like that - but look at the serial number and you can see the difference between a 1 and a 2).  Date of manufacture - Feb 1967.  
   

Purchaser tips:

The outside shell of the helmet weathers wear very well.  It shouldn't have any scratches or gouges.  There should not be any names stenciled onto it - this would be abnormal. Look for any aging on the neck skirt.  However, if you want one of these, but it no matter what condition you find it in.

 The lowest end GSh-4MS helmet is so rare that price is almost beyond issue.  IF you can find one, be prepared to pay at least $1000 and for the model shown here (in incredible condition) the collector paid $1700.
Usage:

The GSh-4MS was used in the flight testing of at least the MiG-17, MiG-19, MiG-21 and probably in the MiG-23, MiG-25, MiG-27, and Su-17/20/22.