Firearms

MBAssociates Gyrojet · Deep Dive

MBAssociates Gyrojet

A 13 mm Gyrojet is a destructive device unless its serial falls inside one of four ranges ATF prints — and at one foot from the muzzle the round carries about four and a half foot-pounds, less than a thrown baseball.

The rocket-firing pistols and carbines MBAssociates built in San Ramon from 1962: the company and its Finjets, the Microjet rocket and what it really did downrange, the hammer that drives the round backwards onto a fixed pin, the die-cast look, every variant with comparison plates, ATF's serial ranges, Vietnam and James Bond, and the upkeep of a zinc-framed gun whose ammunition cannot be replaced.

Photo: Gyrojet at the National Firearms Museum by Joe Loong · CC BY-SA 2.0

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    Volumes

    1. Vol 1 MBAssociates — Two Nuclear Engineers, a Nike Site, and a Rocket That Became a Pistol Robert Mainhardt and Art Biehl, the Finjet and Lancejet that came first, the ARPA money that paid for the Gyrojet, and how a profitable defence contractor came to sell a gun it never made money on
    2. Vol 2 The Round — Canted Nozzles, a Tenth of a Second, and a Rocket That Is Slow at the Muzzle How a Gyrojet rocket is built, why it spins, what it actually does in its first thirty feet, and why it hit so badly: the physics set against every published number, with the numbers kept apart where they disagree
    3. Vol 3 How It Works — A Hammer in Front of the Round The Gyrojet pistol's cycle part by part from MBA's two patents: a forward hammer that drives the round back onto a fixed pin, holds it while the motor lights, and is cocked again by the departing rocket; plus the safety, the magazine, the top slide, and where production guns differ from the drawings
    4. Vol 4 The Look — Zinc Die Casting, Vented Tubes, and Why There Is No Breech Why the Gyrojet looks the way it does, argued from how it was made: a gun that is not a pressure vessel, two cast halves bolted together, a row of gas vents that became its signature, and a company that set out to make a rocket look like a .45
    5. Vol 5 Variants and Identification — Model 137 to Mark II Model C Every Gyrojet pistol and carbine family, what the guns themselves are marked, and how to tell them apart from a listing photograph: comparison plates, marking close-ups, and a feature-by-feature table
    6. Vol 6 The Law — Destructive Devices, the 1968 Redesign, and ATF's Serial Ranges Why a 13 mm Gyrojet is a destructive device unless its serial number sits inside one of four ranges on ATF's Curios or Relics List, what the list actually prints in its April 2025 edition, why the 12 mm gun exists, and what a buyer in Michigan should check
    7. Vol 7 Trials, the Screen, and the Market — ARPA, Vietnam, You Only Live Twice, and What Gyrojets Sell For What the military actually did with the Gyrojet, what is documented and what is only repeated about Vietnam, the films and games it appears in, and eighty-four dated auction results, with the reason the ammunition now costs more per round than the guns once cost whole
    8. Vol 8 Handling, Maintenance and Repair — MBA's Own Instructions, a Zinc Frame, and No Spare Parts What MBA told its buyers about loading, misfires and cleaning; why no takedown procedure can be given and what a correct one must respect; the faults auction records show again and again, what causes each on this mechanism, and what can and cannot be repaired