The HK433 was designed by
Heckler & Koch to be familiar to operators with experience using the Heckler & Koch G36 and HK416 platforms. All controls are ambidextrous, and major components are modular, allowing for rifles to be configured in the field as needed. The HK433 has multiple barrel lengths including 11, 12.5, 14.5, 16.5, 18.9 and 20 inches. All of the barrels are cold hammer forged, hard chrome lined with a 178 mm (1-in-7 inch) right-hand twist, six-groove rifling. It features a short-stroke gas piston driven system similar to the Heckler & Koch G36 and HK416, with a gas block regulator adjustment located above the barrel. The non-reciprocating charging handle can be changed to operate from either side of the forestock of the rifle, but does not have a locking recess like the
Heckler & Koch G3 family of weapons. All other primary controls are ambidextrous. It has an interchangeable barrel system and a folding adjustable
buttstock with a three position cheek riser Side-folding the buttstock shortens the HK433 by . The monolithic upper receiver is made of aluminium alloy, and the lower receiver is made of polymer. It is offered with the option of 2 different lower receivers: one with an AR-15 style magazine release button, and one with a paddle magazine release reminiscent of the G36. The HK433 features a STANAG 4694
NATO Accessory Rail at 12 o'clock that is backwards-compatible with the STANAG 2324/MIL-STD-1913
Picatinny rail. At 6 o'clock it features the STANAG 2324/MIL-STD-1913 Picatinny rail. At the 3 and 9 o'clock positions the proprietary "HKey" accessory attachment system, which was used on early versions of the rifle, has been replaced by the more commonly used
M-LOK system. The empty weight of a HK433
Draft STANAG 4179 compliant
box magazine is approximately . == Variants ==