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In 1978, three years after Brazilian Army’s Fábrica de Itajubá (Itajubá Factory) had become part of the IMBEL – Indústria de Material Bélico do Brasil conglomerate, the unit’s Oficina de Protótipos (Prototypes Workshop) decided to give the earlier 9x19mm C.E.70 submachine gun design some additional modifications. The first resulting test specimen, tentatively designated M978, kept the basic wooden lower receiver and firing mechanism topped by a rectangular upper receiver housing a similarly-shaped, heavier bolt, whose longer displacement distance was aimed at reducing the weapon’s cyclic rate of fire. This was finally achieved, coming down to a more reasonable figure of 600-700 rounds per minute. A new, non-reciprocating charging handle made of light alloys was added to the top of the gun, this featuring a wide U-shaped configuration so that it did not interfere with the use of the sights. Empty cartridges ejection was also moved to the top.
While keeping the same wooden lower receiver, this first modified model was given a rectangular upper receiver and bolt. It was still a full-auto-only SMG, with a transversal safe/fire selector button located just ahead of the trigger. The bolt-blocking grip safety lever was kept.
The tubular stock used in the gun was of a detachable type, the actual usefulness of this system being for very long open to question by the author. Adapted M1911A1 grip plates were added to the wooden pistol grip to enhance ergonomics. Magazine catch was a small button flush with the left side of the housing.
An ensuing M978 was completed sometime during the second half of that year, being the last model to make use some C.E.70 components in a somewhat modified lower receiver, the first-noticed change being the moving of the magazine housing to a position closer to the trigger guard, and this resulted in part of the 230mm barrel becoming partially involved by the also-redesigned rectangular bolt. A one-piece, wooden handguard was added to the forward end of the gun.
This variation of the M978 with a rectangular upper receiver featured a button-type, non-reciprocating cocking handle on top. The IMBEL name before the Fábrica de Itajubá markings on the right side of the ribbed receiver is barely visible. Mag catch was moved to the rear of housing.
The prototype’s detachable stock was reshaped to a lowered-position butt plate. This example had a three-position (Safe, Semi-auto, Auto) fire-selector switch above the trigger, while still retaining the grip safety lever.
The same gun in the sunlight. Markings on the magazine housing base read “Protótipo No. 03 (?)”, while those on the upper receiver are (hopefully…) “Sub Mtr 9 M978”. I wish I had a high-res digital camera back then…
Same photo background, different gun: this M978 prototype (No. 3) fitted with a transversal button (Safe/Auto) fire selector above the pistol grip has a perforated metal jacket around the exposed part of the barrel.
The same prototype’s right side. Rounds observation openings were present in all 30-round magazines.
As usual, higher-res pics are available: https://imgur.com/a/BZlhW
