GSG-5 Right
Click for larger picture (Right side view)
FACTS
 Brand  
 MakeGSG
 ModelGSG-5
 Method of operation  
 Semi AutomaticBlowback
 Trigger1 Stage (single action)
 Trigger Pull 25n  (~6.118 pounds)
 Feeding SystemSingle Stack box magazine
 Technical 
 Weight2930grams (6.459 lbs)
 Width53mm (2.086")
 Overall Length855mm (33.661")
 Barrel Length414mm (16.299")
 Twist Rate1:406mm (1:15.984")
 Grooves6
 Sight Radius340mm (13.385")
 Functionality
 Bolt position when firedClosed
 Bolt upon last round firedOpen
 Magazine capacity22 rounds
 Decocking or Dry fireDry Fire
 Field Stripping  
 Tools requiredSlotted  screw driver and hex wrench 
 Small parts retained or loose2 screws Loose
 Ammunition  
 Caliber.22 Long Riffle (High Velocity)
 Energy @ Muzzle~135
 Velocity @ Muzzle~1,235 fps
 Grains40
GSG-5 Left
Click for larger picture (Left side view)
Opinions
 Method of operation
 Blowback is very good, well tested and highly reliable. (it is not the roller blowback of the MP5) the GSG-5 has duel guide rods with duel springs which is substantial for a .22.
 Functionality
 PriceLow ( < $500)
 AvailabilityCurrently Very Limited
 Modularity / Accessories(Coming soon)
 AccuracyVery Good (for a 16" .22lf)
 ReliabilityVery Good (just clean it)
 Ease of field Stripping
 It is not the easiest to clean, and the required use of tools bothers me.
GSG in very good German fashion provides a tool that will do everything you need.
However it is based on the MP5 design so breakdown requires a little work (nothing you would want to do in the field)
 Ergonomics
 Very Good pistol grip and left/right handed safety controls.
The Cocking handle is left and the shells eject right and can not be modified.
Its light weight overall and very well built with quality metal in all the right places.
 Sighting System (Optics)
 Iron sight  (no current lasers or optics in from Germany at this time)
Typical HK rotating drum peep sight, with rear sight adjustments.
 Ammunition
 PriceVery Low
 AvailabilityEvery where
 PunchLowest
 Links  
 http://www.germansportguns.de
 http://www.americantactical.us/
 http://www.gsg-5.de/
 http://en.wikipedia.org/wiki/GSG-5 
  http://www.cci-ammunition.com/ballistics/detail.aspx?loadNo=0030
GSG-5 Barrel
Click for larger picture (GSG-5 Barrel)

 My ramblings (Over all feelings; Why this Gun; is it worth it):

 I had some friends in town when this gun showed up so we took about 5 bags of guns to the range and picked this gun up and spent the afternoon shooting.  Everyone that shot this gun absolutely loved it and we went through 300 rounds in no time at all.
A gun that's a joy to shoot, and doesn't cost a fortune to own or to use.
A few quick facts because its the first thing everyone asks:
     Its a .22 not a 9mm
     Its not silenced (it just has a barrel shroud so the 16" barrel doesn't look funny)
     Yes its from Germany, and No its not an HK.
     Its less than $500 if you can find one.

In the first week I have shot 600+ rounds through this gun, and it works very well as long as you follow some simple rules.
 - Do not overload the magazines (only put 20-22 rounds in the 22 round magazine).
 - Hold in a shooting position to close the bolt - if the gun is angled the drop safety will hold the bolt open.
 - Clean it before you shoot it.

The magazine capacity is 22 rounds (although mine holds 24 for some reason) and you can easily tell if magazines is loaded or unloaded as both sides of the magazine have cutaway sides to view the single stacked  rounds.  A very cool thing that the GSG-5 does (and the MP5 does not do) is hold the bolt open on last round fired.  However since there is bolt release button it doesn't make anything any faster, but it does keep you from dry firing after last round fired, also by holding open on last round fired cooling happens faster.

One down side (although possibly more safe) is that the trigger will not release the hammer unless the magazine is in.  So making the gun safe by dry-firing it takes a little getting used to; you have to remove the magazine, slap the charging handle down then re-insert the magazine, dry fire and remove magazine.

To compliantly break the GSG-5 down and properly clean it takes a hex wrench and a slotted screwdriver which is much like the real MP5 and is a bit of a pain in the ass.  However the gun is really really good and I refuse to hold this against it (even though the M4 design to separate lower, upper and bolt is 100 times easier).
I still have extra magazines on order and a few other things and hope that they show up soon.  Having a gun with only one magazine means that if anything happens to that magazine and you have a worthless gun.

In short I ordered this gun within a few days of finding out about it and doing the proper research. I was the first person in my state to get one (and one of the first few in the USA to own one).  Being a huge HK fan that enjoys shooting the MP5 and since HK doesn't make the HK94 anymore and I already have the USC45 this gun was an absolute must. 
I wish the importer would have a better way than etching there name into frame and that needs to buffed over a little to give the gun proper fit and finish.  Also make sure you inspect it, clean it and oil it up properly and you should be good for a whole day of shooting (and I'm talking about 500 rounds of high velocity rounds for less than $50).
GSG-5 Sight
Click for larger picture (GSG-5 Rear Sight Drum)


GSG-5 Charging Hanlde
Click for larger picture (GSG-5 Charging Handle)


 Not the best Video of me shooting it (will post a better Video later) Also will teach the
 Person doing the recording not to hold it sideways.