Object Title

Centrefire automatic light machine gun - Experimental Korsak E.M.1

Centrefire automatic light machine gun - Experimental Korsak E.M.1



Object Number



Made at Enfield, 1947. Transferred to IWM (date unknown) Transferred to MoD Pattern Room (date unknown). Gifted with Pattern Room collection, 2005.

Physical Description

The Korsak features a relatively heavy barrel and a bipod, but unusually is in 'bullpup' configuration. Conceptually and mechanically the weapon is based upon the German FG-42 automatic rifle, an advanced development of the American Lewis gun designed for paratroopers and credited to Louis Stange of Rheinmetall-Borsig. The Fallschirmjägergewehr 42 was already quasi-bullpup in arrangement, albeit with a side-mounted magazine well. The FG-42 also provided the E.M.1 with its 'piston extension' (operating rod) and rotating bolt carrier group with two-lugged bolt at its head. As a result, it shares the FG-42's closed bolt/open bolt operation modes for semi and automatic fire respectively. This includes the curious behaviour of the striker, which is cocked by the first ¾ inch or so of cocking handle travel before the bolt itself is unlocked and withdrawn by the remainder of travel. Inside, the striker slides rearward within the bolt, which stays in the closed and locked position. The protrusion on the bottom of the striker slides in a ventral slot on the bolt carrier, but in this mode, not far enough back to cam the bolt open and then pull it to the rear.

The sear is acting on the rearmost of two bents on a unique component known as the 'slide'. This functions essentially as a forward extension of the bolt carrier. In the FG-42, the semiautomatic and automatic bents are machined into the underside of the bolt carrier group. In the Korsak E.M.1, the trigger mechanism sits further forward, and the slide compensates for that extra distance by acting as a forward extension to the bolt carrier group. This unique solution to the perennial problem of poor triggers in bullpup firearms obviates the need for a long trigger linkage bar or rod as in traditional bullpups, and is much simpler than the trigger mechanism of the Thorpe E.M.1. In the accompanying photos, the slide has been left inside the body, but its front portion is visible, protruding from under the gas block. This slide features two bents, which interface with twin parallel sears in the trigger mechanism housing (see below). These are manipulated by rotating the selector switch, which raises and lowers them in and out of engagement with the slide.

On Automatic, the right-hand sear is pushed up by the selector to engage with the front edge of the slide, holding the slide, bolt carrier, and striker to the rear (that is, fully behind the slide) to effect automatic fire. Set to 'Rounds' (or 'Repetition'), the right-hand sear is dropped down out of engagement, and the left-hand sear is able to run within the machined track in the underside of the slide. It can now catch the front bent on the slide, holding only the slide and striker to the rear ready for semi-automatic fire.

When the rifle is assembled, the front edge of the slide acts as the automatic bent, placing the slide and attached bolt carrier almost fully to the rear (there is some over-travel to allow easy cocking) in open bolt condition. This assembly is then ready to be released by the right hand sear in the trigger mechanism (see below), after which it is pushed forward by the compressed recoil spring, closes, locks, and releases the striker for the first shot of automatic fire. In semi-automatic mode, the machined bent at the rear of the slide hangs up on the left hand sear. The bolt itself is fully in battery and locked, but the slide and striker are free to travel the short distance required to fire the first semi-automatic shot. This Weaponsman.com post on the FG-42 shows how this works in the context of the simpler direct engagement of the sear with the bents on the bolt carrier. The other significant point of divergence from the FG-42 is in the use of a tappet style short-stroke gas piston to set the working parts in motion. This is surprising given the other similarities with FG-42, and there is no surviving indication of the thought process here. Clearly, the Soviet lineage of self-loading rifles was thought to be superior in this regard.

The adjustable gas regulator features two settings for normal and adverse operation, and can be switched to the latter setting by depressing the detent with the nose of a cartridge and rotating clockwise (from the shooter's point of view). Returning to the many gifts bestowed by the FG-42, we find a set of folding iron sights with a rotating cylinder for elevation adjustment of the rear aperture. Finally, in common with the FG-42 but also other British designs of the period, Korsak's weapon was chambered for the full-power German 7.92 x 57 mm cartridge. The magazine associated with the gun appears to be a modified, rather than scratch-built, example from the Czech ZB-26, the British Bren magazine – itself derived from the ZB-26 – being too steeply curved for the cartridge. The lug/rocker catch system of the ZB/Bren family, also common to the FG-42, was also used. Finally, the (not quickly) detachable barrel with its simple cone-shaped flash suppressor is also derived from the ZB/Bren. The change lever (selector) operates as per FG-42 with its pull-to-engage, pivot to operate lever, but separates fire selection from safety catch. The former is marked 'A' and 'R' for 'Automatic' and 'Repetition'* (see note at end – Ed.), the latter 'F' and 'S' for 'Fire' and 'Safe'.

There is a hold-open device (HOD) behind the magazine catch, which is designed to hold the action open on an empty magazine, and then to automatically close the bolt when the empty magazine is detached. This is in contrast to later British designs, where the bolt remains held open until the magazine catch itself is operated to release the bolt. Interestingly, this does not function when manually operated, as the bolt carrier is not able to travel far enough to the rear to be retained. It is likely that this feature only worked when the weapon was actually fired, giving the bolt carrier sufficient velocity to compress the rubber buffer inside the butt-plate far enough for the bolt to engage the HOD. In addition, the magazine currently fitted to the gun in the National Firearms Centre collection, whilst it has been professionally modified to fit the gun, does not operate the HOD. Specifically, the standard ZB26 magazine follower features a groove that allows the nose of the HOD to slip into it and prevent the HOD from sticking up far enough to catch the front of the bolt. This suggests that, as Ian notes in the video above, the magazine may not be truly original to the gun as it was first constructed. In theory, the bolt could be manually held open by pressing upward on the tail of the hold open device, but this is fiddly to achieve in practice.


Forging, Filing, Machining, Stamping



BarrelLength20.5 inch
BarrelLength520 mm
OverallLength43.5 inch
OverallLength1104 mm
OverallWeight5.58 kg
OverallWeight12.3 lb


Serial Number None Visible


7.92 mm