The Swiss designation STGW 90, is the non-export version of the SIG SG 550 issued to military personal and instructors of the Swiss Confederation. It was produced in Switzerland by SIG Combibloc Services AG.
The STGW 90 is the replacement to the STGW 57, its philosophy is rather different than its predecessor. While the STGW 57 was a one-configuration-all-roles full power rifle, the STGW 90 is a modular intermediate rifle.
The STGW 90 uses a long stroke gas system and bolt similar to the Kalashnikov. The gas system has the 2 modes, normal mode and dirty/cold mode. It has a Kalashnikov style magazine release and is extremely straightforward to disassemble.
The STGW 90 has a “Kalashnikov style” right side charging handle and a bolt catch release on the left side (like an Armalite). This gives the operator a choice, the bolt can be dropped either by pressing the release on the left or by pulling the charging handle on the right.
The selector has semi automatic, tri burst, and fully automatic burst modes. The full auto mode is marked as 20 since Swiss military doctrine mandates 20 round magazines (useful prone shooting). A true non-export SG 550 SGTW 90 selector has a latch to prevent the burst modes from being selected. The white circle is used to indicate that a Swiss military rifle cannot be switched to burst mode, that it is safe to be used for marksmanship qualification.
Swiss gun culture is quite different than American gun culture, one major difference is that military service is compulsory. Significantly many more Swiss serve in reserve than Americans. That being said, almost all Swiss train in marksmanship at some point in their life. Swiss shooting societies, such as the Swiss Shooting Sport Federation (Schweizer Schiesssportverband) play a role in the design choices of their country’s service rifle. This is reflected in the ”full length” barrel and the sight types.
The rear diopter drum has 4 selections:
The front sight has a simple non-adjustable post with a flip up night glow post for use with rear sight number 1s glow dots. The front sight is protected by a ring, the ring is also used to aim. To aim, match the front ring to the middle of the rear diopter.
The STGW 90 has a 5,56 NATO spec chamber, but neutral Switzerland is not a NATO member. Their cartridge is the 5,6mm GP 90, GP 90 standing for Gewehrpatrone 1990 (not at all the same as the 1890 GP90 Schmidt-Rubin cartridge). This cartridge, manufactured by Ruag Ammotech, uses a 63 grain full metal jacket projectile tailored for the STGW 90s ≈1:10 inch twist rate barrel.
The handguard comes with a built in non adjustable bipod. The pistol grip is proprietary, the stock is non adjustable. The advantage of a non adjustable stock is that every Swiss soldier is trained to immedicably be able to shoot any STGW 90 they acquire without worrying about adjustment. Some special soldiers are issued 2 position stocks that adjust to increase the length of pull. Shorter versions of the SG 550 are issued to some special soldiers, some of these have no bipod in the handguard.
Issuing the STGW 90
Swiss active duty and reserve soldiers train with and are issued this the STGW 90. The other way to be issues this rifle is to be federally recognized as an instructor. The rifle is issued to instructions in 5 year increments from the central government to residents of any canton who meet the requirements. STGW 90 rifles remain Swiss government property at all times.