Notice: Because of the lack of authoritative sources, this article is just a compilation of things I've learned when reading internet forums. All sources are in the References below. No infringement is intended; forums just tend to lose data eventually and this article is meant as a mirror for the information.
The Suhl-150 is an East German single-shot rimfire rifle with a solid reputation for accuracy. They became somewhat available for a while in the late '00s, when Century Arms got ahold of a decent number of them.
My particular Suhl came without a rear sight, which is a common issue. Finding sights for a Suhl isn't easy, but it's not insanely hard either.
Suhl weapons are named for their region of origin: Suhl, East Germany. There are a number of famous gun manufacturers in this city, but if you're here about the Suhl-150, then it's because you're interested in Merkel. It's presently mostly famous for Merkel drillings and shotguns, which are elaborately engraved and valued at over $10k apiece. Their engraving is actually more famous than the gunsmithing. Brands of rifles and shotguns known to come from the Suhl region include Merkel, Simson, Sauer and Haenel. These are commonly called "Suhl", because they're marked with the town name as well as the manufacturer's - e.g. "Simson, Suhl". Prior to the East/West split, the Suhl region was Germany's gun manufacturing area.
The world-famous Anschutz firearms were originally built in the town of Zella-Mehlis, which is 4km away from the city of Suhl. In 1945, Anschutz moved their operations to West Germany, and apparently some of their folks and know-how remained behind in the East German city of Suhl.
Derivation of the Suhl Action
The Suhl action is said to be the same action which Anschutz later developed into the Match 54. However, other folks have stated there's no similarity between the actions.
The Suhl 150 has been used in Olympic biathlons, but not for precision events. The Suhl action-rifle was used in biathlons by some members of the East German Olympic team, and has held a long service life. There were also a very limited series of rifles for the East German biathlon team, where the action was activated by the pistol grip. A notable German biathlete using the Suhl rifle was Frank Ulrich, in the 1980s.
The model number should be in the action. "Don" states that "all of my Suhl 150's are stamped 'Model 150 Standard' w/ 'Made in GRD' directly under it, on the left side of the receiver. The serial number is located on the forward left side.
About the Suhl 150
The Suhl 150 was actually made by the Merkel company, after the Berlin Wall went up. Purportedly the last of these rifles were made in 1992, after which point Merkel went back to drillings and other premium rifles. One theory on why the Suhl 150 is no longer produced is that its action infringes upon Anschutz's patents, which became enforceable once Germany unified. However, this theory conflicts with the later purchase of production rights and tooling by Ernst Thalmann Company AG. If infringement were an issue, the new company wouldn't have been able to build these rifles without Anschutz's blessing.
The first-gen Suhl 150's were built in the 1970s and imported/distributed by Davidson's.
The Ernst Thalmann Suhl-150's were produced with a modified stock design. This new design featured an adjustable comb, and the rifles were imported by Century Arms. No substantial comparison vs the original Suhl 150's appears to have been made.
Design of the Suhl 150
The barrels are pinned and press-fitted, as opposed to threaded.
The factory barrel's twist rate is purportedly 1:19.
Williams Precision, Inc is purportedly the only source of Suhl target rifles. He customizes existing imported rifles, as opposed to building brand new rifles. There are many changes from the factory version, many of which are attributed to Tim McWhorter.
Gary Letnes in Mesa, Arizona is known to make shim kits for the Suhl-150 to correct headspace issues with the barrels.
Butch Hongisto is known to have shims and has the knowledge to install and shim the barrels.
Sights - I've heard 10mm, 11mm, and 3/8" as the dimensions for Suhl 150 rails.
These pictures came from a post on Rimfire Central, where "mistermike" posted them on behalf of "Renegade". They are mirrored here not because I'm taking any credit for them, but because too many times information like this disappears over time as hosting providers change, etc.