The rollers soon compress entirely into the bolt head, clearing the locking recesses of the barrel extension, and both parts now continue rearward together, opening the breech and actuating the extraction and feeding cycles.

Based on the geometric relationship arising from the angles of the roller contact surfaces of the locking piece and the barrel extension recesses, the recoil of the bolt head is delayed by a ratio of 3:1 for the 5.56×45mm NATO chambering.

The lever essentially ratchets into place with friction, providing enough resistance to being re-opened that the bolt carrier does not rebound.

The reliable functioning of roller-delayed blowback mechanisms is limited by specific ammunition and arm parameters like bullet weight, propellant charge, barrel length and amount of wear.

For obtaining a proper and safe functioning parameters bandwidth Heckler & Koch offer a variety of locking pieces with different mass and shoulder angles.

The angles are critical and determine the unlock timing and pressure curve progression as the locking pieces act in unison with the bolt head carrier.

The rifle is disassembled into the following components for maintenance: the receiver/barrel, stock with return spring, bolt assembly and trigger pack in pistol grip.

The firearm is equipped with a relatively low iron sight line that consists of a Drehvisier a rotary rear drum and hooded front post.

The rotary drum features an open V-notch (numbered 1) for rapid target acquisition, close range, low light and impaired visibility use and three apertures (numbered 2, 3 and 4) used for: 200–400 metres (219–437 yd) in 100 metres (109 yd) increments for more precise aiming.

The receiver housing has recesses that work with STANAG claw mounts/HK clamp adapters (standard with the HK33, G3, G3SG/1 and MP5) used to mount day (typically the Hensoldt 4×24 telescopic sight) or night aiming optics.

During its production life the rifle has received several minor improvements (these modified weapons are sometimes referred to collectively as the HK33E).

The fixed stock was strengthened and the synthetic forearm replaced with a handguard that allows a lightweight bipod to be attached and stowed into two grooves at the base.