The MG17 is one of the lesser-known German machine guns used in WWII, used for aircraft armament. Mechanically, the MG17 is basically the same as the MG15 ground gun, but with some aircraft-specific features like propeller synchronization, belt feed, pneumatic charging, and of course no grip or shoulder stock.
Developed at Solothurn and produced by Rheinmetall, the MG17 was intended for fixed mounts in aircraft, while the MG15 was used for manned flexible mountings. The MG17 was built more heavily (approximately 28 pounds unloaded with the necessary controls for remote operation) and fired at a higher cyclic rate of about 1200 rpm. Its belt feed was necessary for practical use, since fixed mounting points in the wings or nose of an aircraft could not be reloaded in flight.
One of the interesting details of the MG17 was its use of a hybrid open/closed bolt method of operation. The MG15 is strictly an open-bolt gun, and the designers wanted to retain the feature of having the bolt remain open when firing to improve cooling. So when the gun’s trigger is released, the bolt will be held in the open position. However, it does not use a fixed firing pin. In the MG15, the firing pin is cocked during forward travel of the bolt, and released immediately upon bolt locking. In the MG17 (when installed in synchronized mounts), the actual release of the firing pin was interrupted by an oscillating block timed to the propeller shaft. This meant that pulling the trigger would cause the bolt to chamber a round regardless of the propeller position, and if the prop was blocking the muzzle the gun would wait with the round chambered until the prop was clear, at which point the firing pin would strike and the firing sequence would resume.
The belt feed for the MG17 was made in the form of a detachable feed block, which was mounted to the gun’s receiver in the same position as the double drum on the MG15. We received an email from a reader who has gotten his hands on the belt-feed module from an MG17 that was installed on an Me-109 that crashed in Latvia, and spent quite a bit of time restoring it to functional condition. His goal is to adapt it to his registered MG15 machine gun, and we’re not sure how feasible that will be. The parts are heavily pitted from 70 years in the dirt, but he says everything appears to be intact and functional. If anyone know more about the specific differences between the MG15 and MG17 receivers, we (and Brent, who owns this piece) would appreciate any information!
He did send us a handful of photos showing the belt feed device, which are interesting to look at. The mechanism is based around a rotating spindle, similar to the Schwarzlose HMG. A ratchet in the front section was used to rotate the spindle at the appropriate times to feed new cartridges. The belt used for these guns was the Gurt 17/81 – the same as used in the MG81, and slightly different from the belts used by the MG34 and MG42 ground guns.