Why the MP28 Was a Separate Design, Not Just a Modified MP18

The common story on the Schmeisser submachine gun line is that the MP28 is just an MP18 with a box magazine bolted on instead of a drum. In a video from Forgotten Weapons, Ian McCollum sits down with Bas Martens, author of "The Real Schmeissers," to show why that version of events leaves out most of what actually changed.

Snapshot

Martens walks through an MP18 converted to a box magazine alongside a purpose-built MP28, pointing out differences in barrel screws, ventilation hole counts, magazine housings, sights, and recoil springs. His core point: these are two distinct designs built around the same basic layout, not one gun with a parts swap, and the timeline of the conversions is later than most people assume.

Key points

• Barrel attachment moved. The MP18 used a rear screw to hold the barrel, later paired with a lock screw; the MP28 relocated that screw forward, which cost it a row of ventilation holes along the barrel shroud.
• Magazines aren't interchangeable. Police and commercial MP28 magazine housings are stepped differently, so Martens notes a magazine from one won't drop into the other, and he says he hasn't found a documented reason why.
• Single-feed by inheritance, not choice. Martens explains Schmeisser's early guns used Luger-derived single-feed magazines, and even after experimenting with double-feed designs, he patented a return to single-feed, a decision Martens says Schmeisser justified on feeding theory later proven unnecessary.
• Fire control and springs changed. The MP28 added a selector for semi-auto and full-auto fire plus a new recoil spring and guide rod, replacing the MP18's auto-only trigger group and its notoriously fiddly internal spring.
• Timeline correction. Martens dates the German police drum-to-box conversions to the early 1930s, not the early 1920s as commonly believed, tied to when Schmeisser's magazine patent became available.

Quick take

For anyone who assumed the MP28 was a minor update, this breakdown from Forgotten Weapons makes the case that it's closer to a parallel design sharing a family resemblance. Worth watching for the mechanical detail alone.

Watch the full video: Forgotten Weapons