Berlin-Lübecker Maschinenfabriken and hammer-forged barrels

Cold hammer forging of small-arms barrels — radial hammers working a blank over a mandrel so that bore, groove, and rifling are formed together — is now the ordinary method for military rifle barrels. English collector pages often credit Berlin-Lübecker Maschinenfabrik (BLM) in Lübeck as the inventor, and others credit postwar Steyr or GFM. Neither caption is adequate. The later research note on this site, “Where hammer-forged rifle barrels originated,” sets out the sources. This page is the workshop companion: what the process does to steel, and how to describe a barrel on a K98k.

What the process does to steel

Hammer forging work-hardens the bore surface, refines grain along the tube, and leaves residual compressive stress in the rifling. For a service barrel that is an advantage: wear resistance, a smooth groove surface, and consistent dimensions from a mandrel rather than from a worn broach. That is why the method survived the war and became the NATO-era standard.

Why Steyr and GFM are named so often

After 1945 the machines, patents, and people moved. Bruno Kralowetz’s GFM in Steyr commercialised barrel-forging equipment from about 1950. Later writers, seeing Steyr production and GFM catalogues, dated the invention to Austria in the 1950s. That is a history of postwar manufacture. Collectors reading a 1938–44 K98k should not assume a hammer-forged tube is anachronistic.

A duv barrel on a byf rifle can be correct wartime logistics. It is not proof that BLM invented cold hammer forging.

What this means on a rifle

A hammer-forged wartime barrel is not a substitute for matching numbers, and it is not automatically more accurate than a well-cut 1938 tube. Record the barrel maker, the date if present, and whether a lead slug shows sloped (forged) or square (cut) groove shoulders. Do not polish the muzzle crown to ‘improve’ it. For origin, Suhl, Sauer, Appel, and GFM belong in the note as well as Lübeck.

Read the origins article before repeating an English Wikipedia caption that BLM invented the process.