Tabic Of Contents


Introduction 5

Chapter 1

Basic Description 9

Chapter 2

Physical Differences 15

Chapter 3

Sequence Of Operation 21

Chapter 4

Modification To Weapon 35

Chapter 5

Parts To Be Manufactured 43


The purpose of this manual is to present the necessary engineering data, manufacturing procedures, and machinist drawings for conversion of the semi-automatic HECKLER AND KOCH 94 (HK-94) carbine into a selective-fire weapon, providing both semi-automatic and fully automatic fire at the control of the firer.

In the modified condition as outlined in this manual, the HK-94 will function in basically the same manner as its military counterpart, the HK MP 5. The rate of fire experienced with the HK-94 conversion approximates the same as the MP 5, which is around 800 RPM.

Minor design changes incorporated in the commercial HK-94 have made the exact duplication of the military MP 5 version impractical. However, the information presented in this manual will explain and show these differences, as well as providing the information required for successful conversion.

Heckler & Koch is one of the Free World's most recognized and respected suppliers of military and sporting weapons, and the HK-94 has the distinction of being one of the finest and most accurate semi-automatic "look-alike" guns on the commercial market today. The HK-94

has been engineered along with its military counterparts to be an integral part of a diversified weapon system which incorporates the use of many common parts and interchangeable assemblies among its various models in an effort to reduce world-wide logistical supply problems resultant from such widescale employment.

Along with other notable semi-automatic carbines such as the UZI and STERLING, the HK-94 shares a common evolution in that each of these were originally engineered and produced as selective-fire weapons intended for military and security use. In response to the growing demands of the U.S. shooting community for paramilitary type weapons, each of these weapons were redesigned and introduced into this country as conventional rifles and carbines.

Under Federal guidelines, the MP 5 in all of its variations are . restricted regarding importation into the U.S., and can be distributed only to authorized military and police organizations, and also on a limited basis as restricted dealer samples to Class III dealers who supply the above mentioned agencies. Civilian shooters living in states which allow ownership of Title II firearms find themselves in the position that they cannot purchase or own a factory produced MP 5. However, under the same set of Federal guidelines, provisions are made that the individual owning an HK-94 may convert their own weapon into a selective fire MP 5 equivalent by following the ATF Form I registration procedure. Shooters desiring ownership of an "HK-94 conversion" may apply for transfer under procedures of ATF Form 4

(on intrastate transfers) if the weapon is being purchased in the selective-fire condition as performed by a licensed Class II Manufacturer. Individuals wishing to purchase a converted 94 from out of state dealers (interstate transfer) must find a Class III dealer in their state of residence who will have the weapon first transfered to that dealer on ATF Form 3, and then in turn transfer the weapon to the individual on ATF Form 4.

The cost for transfer to an individual at this time stands at the long established rate of $200.00. This is a one time tax which is required to allow ownership of a Title II weapon. Laws concerning the ownership of Title II weapons vary from state to state, and also may be regulated on a county or even city level. Before attempting any modification to the HK-94 or any other weapon for that matter, consult the nearest regional ATF office, the local District Attorney's office, and the local police or county Sherriff's Department for local laws concerning ownership of Title II weapons. One word of caution concerning unregistered conversions is that Federal law provides penalty for illegal conversion up to and including a fine not to exceed $10,000, and incarceration not to exceed 10 years. The ownership of a weapon of this type puts a great responsibility on the part of the owner, and it is imperative that it be done in accordance to all laws and regulations.

Hk94 Telescoping Stock

Vie HK-94 A3 selective fire SMG shown with the stock in the retracted position. 800 rpm 9mm provides good accuracy, firepower, and control. fig, j

The HK-94 A3 is a lightweight modem carbine designed after the UK MPS SMC. Note stock in the extended position. fig. 2

Basic Description

The HK-94 is the commercial version of the MP5 submachine-gun produced by the firm of Heckler & Koch, GMBH, Oberndorf am Neckar, West Germany. The MP5 was developed from the G-3 battle rifle, which uses the same method of operation. The MP5 was adopted in 1966 by the police and border police forces of the Federal Republic of Germany, and remains in use to this date. The MP5 also has been purchased by various military and police organizations worldwide, including several in the U.S..

Variations of the MP5 and 94 currently in production are as follows:

HP5 A2

Fixed stock, 680mm overall length, 225mm barrel length


Retractable stock, 490mm overall length retracted, 660mm overall length extended, 225mm barrel length HP5 SD1

Silenced, receiver end cap, no butt stock, 550mm overall length, 146mm barrel length HP5 SD2

Silenced, fixed stock, 780mm overall length, 146mm barrel length


Silenced, retractable stock, 610mm overall length retracted, 780mm overall length extended, 146mm barrel length HP5K

Vertical foregrip, no buttstock, 325mm overall length


Same specifications as the MP5K, except there is only a very small front and rear sight provided for undercover deployment. 94 A2

Fixed" stock, 890mm overall length, 420mm barrel length

94 A3

Retractable stock, 700mm overall length retracted, 865mm over all length extended, 420mm barrel length

NOTE: All of the MP5 series SMG's can be fit with burst limit selectors which limit the number of shots fired with each pull of the trigger to 3, 4, or 5 shots. This is produced by using a ratcheting device which eliminates conventional full-auto fire.

All variations of the MP5 and 94 are recoil-operated, featuring a stationary barrel and delayed roller-lock bolt system of the type used in the HK G3, 7.62mm battle rifle. This bolt system has been successfully used for nearly 30 years and is a result of the earlier bolt system pioneered by Mauserwerke at Oberndorf for the innovative StG-45 assault rifle of WWII origin.

The MP5 submachine-gun and selective fire HK-94 as presented in this manual operate from a closed bolt. This method of operation is rather uncommon in the construction of SMG's, although it is not unique. Most submachine guns fire from an open bolt, utilizing a fixed firing pin and using a blowback operated mechanism which requires no locking device to secure the bolt into the receiver during detonation. Similar weapons of this type (such as the UZI, STEN, THOMPSON M1A1) depend on a heavy bolt mass to retard and delay the rearward movement of the bolt until chamber pressure drops to a safe level. In the closed bolt HK-94 and MP5, the bolt incorporates a floating firing pin and dual rollers which cam outward into matching recesses in the receiver, locking the bolt and carrier in the "closed" position. The weapon is readied for firing by manually retracting the cocking lever and releasing it, which allows the bolt and bolt carrier to slam forward, the hammer being held rearward by the sear. The forward movement of the bolt strips the top cartridge from the magazine and feeds it into the barrel. The weapon is now ready to fire, and manipulation of the selector determines the mode of fire. By utilizing a closed bolt mechanism in the MP5 and HK-94 the firer experiences less vibration, improved accuracy, faster lock time, and a lighter overall weight as opposed to most SMG's of this caliber. The two principle criticisms of closed bolt SMG's are their increased price due to the complexity of their mechanisms and the possible danger of "cook-offs" during extremely high volume firing. Although virtually non heard of, the high temperature of the barrel chamber can radiate through the live cartridge and presumably detonate the priming compound when a live round is chambered and left in a hot barrel.

The export version 94 produced by Heckler and Koch and imported into this country retains virtually all of the original MP5 parts and/or assemblies, deleting and modifying only those parts which provide full automatic capability. Also, a longer barrel is incorporated in accordance to Federal law. The modifications required to the 94 to produce selective fire functioning are confined to the hammer, bolt carrier, trigger housing, and grip assembly. In addition, a secondary-sear/release-lever assembly must be manufactured to complete the conversion. An engineering change regarding the manner of attaching the entire trigger housing to the receiver prevents the use of standard MP5 select fire "drop-in" components, necessitating the modification of a few of the existing parts and requires the addition of some new parts.

One noticeable difference in the MP5 and 94 is that the magazine release on the MP5 pivots forward to release, whereas the release of the HK-94 must be depressed from right to left. This is an unfortunate change since the original version as found on the HP5 is much better. It is possible to customize the magazine release with a commercially produced unit called the "TAC-LATCH", which provides a somewhat more accessible release lever.

Accessories marketed by H&K and aftermarket suppliers include various telescopic sights and mounts, point firing and laser aiming devices, brass catchers, 15 and 30 round magazines, slings, and image intensifier sights.

These weapons have been proven to be very accurate, owing a great deal to the closed bolt mode of fire, and are rugged and functional under adverse conditions worldwide.

An interesting note from a design, manufacturing, and supply viewpoint is that HECKLER & KOCH has based various weapon systems around a standard trigger group assembly. This alone provides users of these systems with a logistical advantage over other systems requiring different component parts for each type of weapon.

Hk94 Explosive Parts

HK-94 A3 shown field stripped into its major components.

Top Level Retaining Lever

Barre* Down pm

Cocking lever housmg Retaining cUo **h bush Front Right hotter Front sjgnt Clamping sleeve Eyebo*

Cocking tew aupoon with collar CocKmg lev*/ Axle lor COCking lever Catcn bofl

Spring for catch bcrft Cap

Cartndge cam oeftedor «•vet carmoje case oeftector Adjusting sc*ew Compression sonng


121 Catch bolt 1.22 Spnng tar catch bo« 123 Rear sight Support 1.24 Rear s«ght cyWnder 125 Wisher

1 26 Toothed tocK «¿she* 127 Clamoing screw 1 28 Magazine catch 1 29 Spnng lor magazine catch

130 Contact piece

131 Pus* button

I 32 Clamping sleeve 1 33 Magazine rpteas* lev*'

release >eve'

Asaembfy Group 2 Bolt

2.1 Bofi r>eao earner

2.2 Stop pm

2 3 Clamping s*eeve 2 4 Bon head

2 5 Extractor

2 6 Extractor spnng

2 T LocK>ng roller b

2 9 Clamping s*eve

2 10 wOCfcmg piece

2 11 FWwig pep spnng

2 12 Fmngpin

2 13 Reco* spnng

2 14 Reco»i sprmg gurte rod


2 16 Stop pm lo< recol Spring 2.17 Rrveting pm


Tngger houung assembled ^withotf illustration)

Locking pm lor pisto« gro Selector *e*er


3 21. Tnpgerhousmg 3 2.2. Hammer 3 2 3 Pressure shank tor hammer 3 2 4 Riveting pm lo* pressure shank

2.2 5 Compress»^ SO^ng lor nam/ne^ 3 2 6 Aiie tof harrmer 3 2 7 Aa* for tngger and catch 3 28 Tngg«r 32 9 Sear 3 2 10 Trigger Dolt 3 2 11 Spnng tor tngge* DOT 3 2 12 Ciamcmg siee** 3 2 ^ 3 Eibovp sonng for t'»gge' 3 2.14 Catch

♦or catch 32 16 Distance sleeve 32 17 Axle lor ejector 3 2 18 Spnng ring 32 19 Elector 3 220 Ejector sonng

3 2.21 Release »ever

Assembly Grouo 4 Fued Butt stock

4.1 Butt stock

4 2 Back plate

4 3 Locking pin tor Dutl slock

Assembly Group 6 Handguard

61 Handguard

6.2 Locking p»n Uy h^rtogoa/e

Aaaembiy Group 7 Magazine 7.1 Magazine hOusmg 72 *otto*er 7 3 Fottowrer sonng 7 4 Spnng noor pore ^ 7 5 Magazine floor piate

AeeemWy Group 8 MuHk jS purpose carrying *J*tg

81 Carrying Ming ; • fesf 6.2 Carbine nook

S.3 Double eye ; gJ 8 4 Buckie a 5 Spnng hook



5 m/n /WP5 A2 Heckler and Koch sub-machinegun

Physical Differences

This chapter examines and notes the physical differences between the MP5 and HK-94. Although not directly needed as far as the actual conversion is concerned, it is of academic interest from a design viewpoint to be knowledgable of the differences. Each sub-title will discuss the differences of the respective parts.


Both the MP5 and 94 utilize a push button magazine release located on the right side of the lower receiver. The MP5 also features a vertical release lever located directly below the push button assembly. The vertical release lever is very desirable, and permits magazine removal with the left hand without ever changing the grip of the firing (right) hand. The lever is manipulated with the thumb of the left hand.


The MP5 uses a total of two locking pins to secure the assembly of the receiver, grip assembly, and buttstock. The rear locking pin passes through the buttstock housing adapter, receiver, and upper rear portion of the grip. The front of the grip has two ears which has a central hole passing through them. These ears straddle the lower rear portion of the magazine housing and the second locking pin passes through the alignment holes in both parts. By having the grip attach to the magazine housing in such a manner, the entire grip/trigger group can be sv/ung down when field stripping. The grip of the HK-94 does not have these ears, instead a machined block welded into the lower front of the grip has a lug which engages a machined slot in the magazine housing on the back side. Only one locking pin is used to assemble the HK-94 in both the A2 and A3 versions.

Because of this particular engineering change in the HK-94, an exact duplicate MP5 type conversion using parts from it is impossible, partly because of the machined block welded in the grip changes the location of the drilled hole through which the secondary sear (referred to as catch by HK) and torsion spring and spindle assembly are secured in the trigger housing. This relocation of the hole prevents the use of the factory made catch.

One other change noted in the grip is the addition of the third selector positioning detent in the left side of the assembly. The MP5 fire control positions are identified as "S" or "0" for SAFE, "E" or "1" for SEMI, and "F" or "2" for FULL AUTO firing. The two detents in the HK-94 will be in the same relative position as those of the MP5, the third position for full automatic fire being deleted.


As previously mentioned in the Grip section, the location of the hole retaining the sear torsion spring, spindle, and axle is moved rearward in the 94 trigger housing, preventing the use of original MP5 parts. A second difference in the 94 trigger housing is the addition of a trigger limit stop pin, which acts to limit the upward movement of the rear portion of the sear, thereby preventing the sear nose from moving low enough not to intercept the hammer.


The MP5 hammer features two machined and ground engagement notches. The lower notch engages the primary sear, while the front notch engages the secondary sear (catch). The hammers being provided in the HK-94 carbines received are found having a factory MP5 hammer with the two notches, or they may be received in which the MP5 hammer has had the front notch removed by grinding. The depth of the notch between a MP5 hammer will be different in relationship to the centerline of the hammer axle hole when compared to the same measurement from a reworked hammer as used in this conversion. For this reason, the conversion described in this manual assumes that the user has a "semi-only" factory reworked hammer, and the secondary sear notch will be ground as shown in the accompanying drawings. If a MP5 hammer is supplied in a HK-94, this conversion will work, although the profile on the secondary sear block and release will be slightly different. If this is the case, make the release lever and secondary sear assembly as drawn, and hand fit the contact area of the lever and block until the assembly disengages from the hammer when dry firing.


The MP5 utilizes the use of an auto sear, denoted in the H&K drawings as a "catch". This is the part which pivots on the catch axle to intercept and hold the hammer in a rearward position during each firing cycle, both in semi-automatic and fully automatic firng. This part is contacted by a separate release lever which pivots independantly from the catch. The catch is deleted from all semi-auto HK-94 carbines.


The MP5 utilizes a separate release lever which is contacted and pivoted forward by the bolt carrier during each firing cycle. Unlike the release lever used in this conversion which is a part of a rigid assembly consisting of the secondary sear, spindle, and release lever, the release lever in the MP5 is much longer and pivots on the hammer axle. The longer length of the lever in conjunction with the angle of its interception by the bolt carrier provides good leverage and a very smooth movement. The release lever is not present in any of the HK-94 carbines.


The bolt carrier of the MP5 and the HK-94 both are apparantly produced identical to each other, the only difference being that the camming radius that contacts the top of the release lever is machined out in the HK-94 bolt carrier, so as to prevent its use in conjunction with an auto-sear mechanism. This method of using one particular part as the basis for both weapons is novel also in that at any given time in the various production runs of 94, the MP5 bolt carriers can simply be removed from stock and the minor operation of removing the contact radius be performed at that time.

Grip Assembly

1. Grip Assembly

2. Trigger Assembly

3. Locking Pin

4. Plastic Grip

5. Panhead Screw

6. Lock Washer

7. Selector Lever


The grip assembly (1) is the housing in which the entire trigger assembly is inserted in assembly. The trigger assembly (2) fits securely into the grip frame, and the selector lever (7) is inserted through the left side of the grip, passing through a corresponding hole in the trigger assembly. The selector lever is positioned by the firer for "SAFE", "SEMI-AUTOMATIC", or "FULL-AUTOMATIC" modes of firing.

The plastic grip (4) is positioned over the grip assembly and is held by means of a panhead screw (5) and lock ■washer (6). The entire grip assembly is fixed to the receiver by means of a locking pin (3).

Semi Auto Grip Assembly

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Sequence Of Operation

To ready the HK-94 for firing, first insert a loaded magazine into the magazine well until it is firmly seated, being retained at this time by a spring-loaded catch which locks it in place. The firer then retracts the cocking handle found on the left forward side of the receiver fully rearward, then releasing it sharply, which in turn under the influence of the heavy recoil spring causes the bolt and carrier assembly to slam forward, stripping a live cartridge from the top of the magazine and feeding it into the chamber of the barrel. At the time the cocking handle was retracted, the hammer was rotated rearward, and the sear nose and secondary sear both under tension from their respective springs move in position against the hammer in such a manner that upon the forward movement of the bolt and carrier assembly, the hammer is intercepted and held in a "cocked" position by the sear. The secondary sear/release lever assembly (to be hence forth referred to as auto-sear in this chapter) at the time of final forward movement and locking of the bolt and carrier assembly is forced to pivot forward after being contacted by the radiused portion of the tripping block. This movement of the auto-sear is repeated during each cycle of the weapon, regardless of the mode of operation.

With the auto-sear forward at this time, the primary sear is holding the hammer rearward.

Upon the forward movement of the bolt and carrier assembly, the dual locking rollers in the bolt head are in a recessed position until the bolt positively positions against the breech of the barrel, and the continuing forward movement of the locking piece and bolt carrier against the stationary bolt cam the rollers outward into matching recesses in the receiver wall. The weapon at this time is in a ready condition, and the selector would be positioned at the uppermost setting for "safe". In this position, the rear extension of the trigger is prevented from upward movement by a machined notch in the selector shaft. The weapon is to be carried in this mode until ready to fire.


If the firer chooses to fire single shots, the selector is rotated down to the middle detent, identified as "F" or "1". When the trigger is operated by depressing rearward, the sear is rotated down at the front and out of engagement with the notched portion of the hammer. The rear movement of the trigger is stopped at the proper point by a corresponding notch in the selector shaft. When the hammer rotates to fire the round, the spring-loaded sear slips forward under the influence of the trigger bolt spring, and the tail of the sear drops off a fixed step located on the top, rear area of the trigger. This is called the "pull-off surface". With the firer still holding the trigger down, the hammer strikes the firing pin, detona ting the primer and cartridge. When the chamber pressure reaches a safe level, the forces against the bolt cause the rollers to move out of their recesses in the receiver, and the residual pressure in the barrel causes the bolt and carrier assembly to move rearward, extracting the empty case at this time. The movement of the bolt carrier rearward in turn forces the hammer to rotate to the rear, the auto-sear and primary sear rising and intercepting the hammer as the bolt and carrier reverse direction under pressure of the recoil spring. Again, a live round is stripped and chambered. Since the tail of the sear was pulled off of the step at the rear of the trigger during the initial firing, another shot cannot be fired until the firer first releases the trigger. When the trigger is released, the rear end or tail of the sear is allowed to rise, the trigger bolt spring forcing the sear backwards up on top of the step of the pull off surface. The sear has an elongated hole through it in which the trigger axle is positioned. When the trigger is depressed again another round will be fired, the cycle repeating itself as described.


When the selector lever is rotated down to the "A" or "2" position, fully automatic fire will result. Depressing the trigger firmly in this position allows the sear tail to rise so high that the front of the sear is positioned low enough so that it does not intercept and hold the hammer after the initial shot. However, the auto-sear catches and holds the hammer after each shot is fired, until a point in which the tripping block in the bolt carrier contacts and disengages the secondary sear from the ground notch in the front of the hammer. By freeing the hammer from engagement with the auto-sear, the hammer rebounds forward, striking and detonating the cartridge. This sequence will continue until the weapon runs out of cartridges, or until the firer releases the trigger at which time the sear nose rises and catches the hammer. The weapon is at this time cocked and merely pulling the trigger will initiate the firing sequence again.

Hk94 Trigger Group Markings
Left side view of Trigger Housing. Note position of Release Lever. Bolt Carrier slamming shut would move the lever forward releasing Hammer from Secondary Sear. Selector manipulation will produce "SEMI" or "FULL" automatic mode of operation. Pig. 7

ro en

Bolt Catch Release Left



1. Bolt head carrier

2. Firing pin

3. Release lever

4. Anvil for hammer

5. Trigger spring

6. Hammer

7. Selector lever shaft

8. Pressure shank & pressure spring

9. Catch (secondary sear)

10. Elbow spring with roller (torsion spring)

11. Trigger lever (sear)

12. Trigger

Full Auto Conversion

The weapon is loaded and the hammer is in the cocked position, being held by the sear nose. The selector lever is in the "S" safe position. In this position the trigger is blocked by the shank of the selector lever and cannot be rotated rearward.

40mm Grenade
Fig. 10

The selector lever fire.

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  • carson
    Is the hk94 semi auto for civilian use illegal in california?
    9 years ago
    How to convert hk94 to full auto?
    9 years ago
  • Annett
    How to comvert a full auto hk 94 bolt to semi auto?
    8 years ago
  • largo
    What part turns a h k 94 to full auto?
    5 years ago

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