The HK36 was an experimental assault rifle introduced by Heckler & Koch in the early 1970s. At the time, research in small-caliber military cartridges had become more popular thanks to the United States' adoption and combat use of the M16 and its 5.56×45mm round. ^{[citation needed]}

The HK36 rifle fired a 4.6×36 mm round whose bullet has a "spoon point" (German: Löffelspitz) designed by CETME's Dr. Gunther Voss. Low bullet weight and the straight-line layout of the rifle reduced recoil, while the high velocity of the round gave it an almost flat trajectory out to 300 metres (330 yd), which was also the limit of its effective range. Beyond that point, the bullet lost velocity very quickly.

The HK36 used H&K's delayed blowback system, with a four-position selector switch for the firing mode. In order from top to bottom, these were safe (marked "0"), single-shot ("1"), full-automatic ("25" or "30") and controlled burst ("3")—however, the weapon was intended to be available with 2-, 3-, 4- or 5-round burst mode.^[1][2]

Ejection of empty cartridge cases was to the right, while the bolt remained open once all ammunition had been expended.^[1]

Early versions of the weapon had a standard detachable box magazine made from stamped metal.^[2]

The method of reloading for the later prototypes was an unusual departure from modern systems, being intended to reduce weight along with eliminating the handling of individual rounds. The rifle had a metal box mounted permanently below the receiver, in front of the trigger guard; this magazine had a side-opening "door" through which a pre-packaged box of 30 cartridges could be inserted once a knob on the rifle had been pulled down.^[1] The box had an open top and bottom,^[1] closed by tape, so that the magazine follower could push the rounds up into the rifle during firing.

As mentioned, early models used a conventional detachable box magazine while later versions had the integral one. In addition, most of the rifles appear to have been fitted with a telescoping stock^[2] of a completely different type than that fitted to most other Heckler & Koch weapons (such as the G3 and MP5), but some are known with a fixed, plastic stock.^[1]

Despite never being accepted for military service, the rifle was notable for introducing the three-round burst concept and integrated optics to Heckler & Koch weapons. The various innovations gave H&K some interesting ideas for the future, which have resurfaced in the Heckler & Koch MP7 PDW and G36 rifle.

• List of assault rifles

• HKPRO

v t e Delayed blowback firearms
Lever delayed	AA-52 Benelli B76 Cristóbal Carbine Danuvia 43M Dlugov FAMAS FN Five-seven FNAB-43 Garanin MAC-58 Sterling 7.62 ST Kinetics CPW TKB-517 AVB-7.62
Roller delayed	Calico M960 CEAM Modèle 1950 CETME Ameli CETME rifle CETME Model L Gerät 03 prototype HK G3 HK G41 HK MP5 HK P9 HK PSG1 HK MSG90 HK SR9 HK UCP HK21 HK33 HK43 HK SL6 HK SL7 MG 45 PTR 91F SIG 510 SIG MG 710 SRM Arms Model 1216 StG 45(M)
Gas delayed	Arsenal P-M02 Grossfuss Sturmgewehr Heckler & Koch P7 M-77B Steyr GB Volkssturmgewehr 1-5 Walther CCP
Hesitation locked	M50 Reising Remington Model 51 Remington Model 53 Remington R51 SIG MKMO
Flywheel delayed	Barnitzke machine gun MGD PM-9
Radial delayed	CMMG MkG
Toggle delayed	Schwarzlose machine gun T1E3 Model 32 semi-automatic rifle
Vector delayed	Jatimatic KRISS Vector