Overview[]
The MC-51 is a British envisioned, albeit designed and produced in the United States, firearm conversion design which aimed at turning HK G3 platform firearms into shortened "battle" carbines.
Although often called the "HK 51," the weapon in-question is not manufactured nor endorsed by Heckler & Koch. However, name fits the HK system for naming firearms at the time of it's original production, with the "5" representing a compact firearm, and the "1" signifying that the weapon was chambered for the 7.62x51mm cartridge.
Development[]
By at least 1989, and overlapping into the early 1990s, special operation units within the United Kingdom, notably the Special Air Service and Special Boat Service, had been undergoing a unformal process of trialing and testing the usage of various recently-produced firearm designs as a way to possibly find a suitable replacer to their aging armoury, which mostly consisted of various HK MP5-series submachine guns, or the long-time serviced L34A1 submachine gun design, which itself had been rooted in the late 1950s. Whilst both options remained popular by their operators, and asides from the factor of firearm design age, other factors were considered to be important enough to further warrant replacement, notably the limited range due to submachine guns often utilizing short barrels, paired with the small cartridges of such designs being deemed inefficient for a majority of non-close quarters situations. Despite this, a preferable design would have been compact still, but boasting superior firepower and penetration capabilities than that of a majority of submachine gun designs.
Since the early 1980s, an American firearms designer who specialized in Heckler & Koch products, named Bill Fleming, had been personally been designing, producing, and manufacturing various modifications and conversion kits for military rifles, notably the H&K G3 platform, with the goal of having the "converted" rifles gain traction on the civilian market under the front company of "Fleming Firearms." A majority of his success came from these personal sales, or for selling various H&K G3 lower receivers ranging from the early "S-E-F" pattern, to the more recent "Navy" pattern ones. Nonetheless, one of Fleming's more well-known designs was what he called the "HK 51," which was essentially a H&K G3 platform firearm which had been "cut down" to roughly the length of an H&K MP5 submachine gun, whilst retaining the full-sized 7.62x51mm NATO cartridge which the original H&K G3 series of rifles had been fitted in. These "HK 51" designs, in some form or another, had been sold on the American market since at least 1984, and were adopted in various names such as the "Fleming Model 51."
At some point, a defence-firm operating in the United Kingdom known as FR Ordnance would be able to contract Bill Fleming to produce a variety of his "HK 51" designs for potential military trials, to which Fleming agreed. Under FR Ordnance, the firearm would be renamed under the designation of "Machine Carbine 51," which is often abbreviated to "MC-51." Although uncertain, it is possible that Fleming further submitted other conversions derived from his personal designs, which could have included what was originally labelled in the United States as the "Fleming Model 51K" or the "HK 51K" under the designation "MC-51K" which, as the nomenclature of the name suggests, would be an even further-shortened firearm, somewhat resembling the front-end of the H&K MP5K series. Another unconfirmed design is one which borrows the integrally suppressed barrel system from the H&K MP5SD series, which is commonly called the "MC-51SD," although as aforementioned, this particular variant is unlikely to exist outside of popular culture, as obtaining such sound-dampening systems would have been highly unlikely to procure in either the United Kingdom, or the United States, where the Fleming had been producing his firearm designs.
Whilst boasting improvements over other in-service firearms at the time, the MC-51 design was never fully integrated into service with any military or special operations unit for extended amounts of time. This was considered due to the compact nature of the firearm utilizing the large 7.62x51mm cartridge, resulting in high-recoil, noise, and concussion, especially within close-quarters situations. The fully-automatic fire mode reportedly made it difficult for users to keep track of their targets.
Ultimately, the United Kingdom would adopt the HK53 series for their special operations units, as a replacement to shortly-lived MC-51 platform, due to 5.56x45mm becoming more universal, and since both firearms are roughly the same size.
Design[]
The design is essentially a cut-down G3A3, close in dimensions to the HK MP5A3. The handguard is also borrowed from the MP5, however, other similar parts such as the stock and pistol grip are taken from various G3 models. Iron-sights are also standard to the G3 platform.
Most models were produced with a telescoping-stock design, similar to the one produced per standard on the G3A4, however, solid-stock models were also available.
Usage of the roller-delayed blowback action is also utilized, much like most other HK products at the time.
Variants[]
|
| H&K G3 Platform | |||
|---|---|---|---|
| Originals | 
| ||
| Heckler & Koch | MIL | G3 • G3A1 • G3A2 • G3A3 (A1) • G3A4 (A1) • G3A5 • G3A6 • G3A6 (A1) • G3KA4 (A1) • G3NA3 • G3SG1 | |
| C&LE | HK11 • HK12 • HK13 • HK21 (A1 • E) • HK23 • HK25 • HK31 • HK32 • HK33 • HK41 (A2 • A3) • HK43 • HK53 • HK54 • HK81 • HK 91 (A2 • A3) • HK93 • MSG3 • MSG90 (A1 • A2) • PSG1 (A1) • SR9 (T • TC) | ||
| Derivatives | |||
 Denmark
|
Gv M/66 • Gv M/75 | ||
 Greece
|
SAR-3 • SAR-8 | ||
 Iran
|
G3A6 | ||
 Luxembourg
|
HSG1 • HSG41 | ||
 Mexico
|
Morelos (A • B) • MSG-90SDN | ||
 Myanmar
|
BA 63 • BA 64 • BA 72 • BA 100 | ||
 Netherlands
|
Armtech 51 | ||
 Norway
|
AG 3 (F1 • F2 • HVU) | ||
 Pakistan
|
G3P3 • G3P4 • PK-7 • PK-8 • PSR-90 | ||
 South Africa
|
R2 | ||
 Sweden
|
Ak 4 (B • C • D • HV • OR) | ||
 Turkey
|
G3A7 (A1) • T41 | ||
 United Kingdom
|
MC 51 (K • SD) | ||
 United States of America
|
FA91 • HK 21 K • HK 51 • SAR-3 | ||
 West Germany
|
Rh4 | ||
Weapons of the United Kingdom  After the Second World War |
|---|
| Infantry Weapons | ||
|---|---|---|
| Melee Weapons | Bayonet | [[]] |
| Survival Weapon | [[]] | |
| Sidearms | Pistol | L9A1 • L18A1 • L47A1 • L66A1 • L102A1 • L105A1 (A2) • L106A1 (A2) • L107A1 • L109A1 • L117A1 • L131A1 • L132A1 • L137A1 |
| Revolver | [[]] | |
| Machine Pistol | [[]] | |
| Close Quarters | Personal Defense Weapon | [[]] |
| Submachine Gun | L2A1 (A2 • A3 • A4) • L34A1 • L49A1 • L50A1 • L51A1 • L52A1 • L80A1 • L90A1 • L91A1 • L92A1 | |
| Shotgun (semi-automatic) | L128A1 | |
| Shotgun (manual-action) | L74A1 (A2) | |
| Primary Weapons | AR | L85A1 (A2 • A3) • L119A1 • (A2) • XL70 • XL73 • XL78 • XL85 • XL86 |
| AC | L22A1 (A2) • L101A1 (A2) • L119A1 (A2) | |
| BR | L1A1 | |
| BC | L100A1 (A2) | |
| Automatic Support Weapons | Light Support Weapon | L86A1 (A2) |
| Light Machine Gun | L4A1 (L4A2 • L4A3 • L4A4 • L4A5 • L4A6 • L4A7 • L4A8 • L4A9) • L108A1 • L110A1 (A2 • A3) • L130A1 | |
| General Purpose Machine Gun | L7A1 (A2) • L19A1 | |
| Heavy Machine Gun | L1A1 (A2) • L111A1 • L114A1 | |
| Long Range | Anti-Materiel Rifle | L121A1 • L135A1 |
| Bolt-Action Rifle | L8A1 (A2 • A3 • A4 • A5) • L39A1 • L42A1 • L96A1 (A2) • L115A1 (L115A2 • L115A3 • L115A4) • L118A1 | |
| Designated Marksman Rifle | L2A1 • L129A1 (w/ L17A1) | |
| Launchers | Grenade Launcher (Attachment) | L17A1 (A2) • L123A1 (A2 • A3) |
| Grenade Launcher (Standalone) | L14A1 | |
| Disposable Rocket Launcher | L2A1 • L72A9 | |
| Rocket Launcher | [[]] | |
| MANPADS | [[]] | |
| Non-Lethal Weapons | Pistol | [[]] |
| Underwater Weapons | Sidearm | [[]] |
| Rifle | [[]] | |
| Explosives | Anti-Personnel Mines | M18 Claymore |
| Anti-Tank Mines | L3A1 • L9A1 (A2 • A3 • A4 • A5 • A6 • A7 • A8) • Mine, Anti-Tank, L14A1 • L17A1 • L18A1 • L27A1 | |
| Practice Mines | L21A1 • L28A1 • L29A1 (A2) | |
| Anti-Personnel Grenades | L1A1 (A2 • A3) • L2A1 (A2) • L13A1 (A2) • L98A1 • L109A1 (A2) • L106A1 • L107A1 • L109A1 (A2) | |
| Smoke Grenades | L35A1 (A2) • L36A1 (A2) • L37A1 (A2) • L38A1 (A2) • L50A1 • L52A1 (A2) • L53A1 (A2) • L54A1 (A2) • L55A1 (A2 • A3) • L64A1 • L65A1 • L66A1 • L67A1 • L68A1 • L69A1 • L70A1 • L71A1 • L84A1 (A2 • A3) • L100A1 • L101A1 • L132A1 (A2) • L152A1 • L153A1 • L154A1 • L155A1 • L157A1 • L158A1 | |
| Practice Grenades | L3A1 (A2 • A3) • L4A1 (L4A2) • L16A1 (L16A2) • L28A1 • L56A1 • L73A1 (A2) • L83A1 (A2) • L108A1 (A2) • L110A1 • L111A1 • L115A1 | |
| Infantry Equipment | ||
|---|---|---|
| Clothing | Backpacks | [[]] |
| Body Armour | [[]] | |
| Bomb Suit | [[]] | |
| Elbow and knee pads | [[]] | |
| Signals & IFF | [[]] | |
| Suits | [[]] | |
| Vests & Webbing | [[]] | |
| Headwear | Communication | [[]] |
| Gas Masks & Rebreathers | [[]] | |
| Goggles | [[]] | |
| Helmets | [[]] | |
| Vehicle Headwear | [[]] | |
| Optics, Detection and Surveillance | Man-Portable Radar | [[]] |
| Mine Detectors | [[]] | |
| Night Vision Goggles | [[]] | |
| Periscopes | [[]] | |
| Rangefinders | [[]] | |
| Surveillance | [[]] | |
| Artillery | |
|---|---|
| Anti-Aircraft Guns | [[]] |
| Anti-Tank Guns | [[]] |
| Anti-Tank Guided Missile Launchers | [[]] |
| Anti-Tank Guided Missiles | [[]] |
| Grenade Machine Guns | L134A1 |
| Howitzers | [[]] |
| Mortars | 51mm L9A1 • 60mm M6(H) (-640 • -895) • 81mm L16A1 (A2) |
| Railroad Artillery | [[]] |
| Recoilless Guns | [[]] |
| Rocket Artillery | [[]] |
| Siege Artillery | [[]] |
| Land Vehicle Weapons | |
|---|---|
| Vehicle Machine Guns | BESA • Bren Gun • Browning M1919 • FN MAG • L4A4 • L8A1 (A2) • L37A1 (A2) • L43A1 • L94A1 |
| 30mm Tank Guns | L21A1 |
| 40mm Tank Guns | QF 2pdr HV • CTA40 |
| 75mm Tank Guns | QF 75mm • Vickers HV 75mm |
| 76.2mm Tank Guns | L5A1 • L23A1 • QF 17pdr • Vickers HV 77mm |
| 84mm Tank Guns | QF 20pdr |
| 94mm Tank Guns | QF 32pdr |
| 105mm Tank Guns | L7A1 (A3) |
| 120mm Tank Guns | EXP-28M1 • L1A1 (A2) • L11A1 (A2 • A3 • A4 • A5 • A6) • L30A1 • XL30 |
| Howitzers | 88mm 25pdr • 105mm L13A1 • 155mm L31A1 |
| ATGMs | BAe Swingfire |
| Aircraft Weapons & Munitions | |
|---|---|
| 7.62mm Machine Guns | L112A1 |
| 12.7mm Machine Guns | [[]] |
| 23mm Cannons | [[]] |
| 30mm Cannons | [[]] |
| 37mm Cannons | [[]] |
| Rocket Pods | [[]] |
| Rockets | [[]] |
| Air-to-Air Missiles | [[]] |
| Air-to-Ship Missiles | [[]] |
| Air-to-Surface Missiles | [[]] |
| Anti-Radiation Missiles | [[]] |
| Cruise Missiles | [[]] |
| Bombs | [[]] |
| Sources | ||
|---|---|---|
| Books | Online | Documents |
| • Full Circle - A Treatise on Roller Locking, R Blake Stevens (ISBN 0-88935-400-6) | https://www.forgottenweapons.com/hk51-the-sas-full-auto-flashbang-dispenser/ | |