During the 1950s, West Germany was faced with the dilemma of rearming with the new 7.62x51mm NATO cartridge that was being fielded by NATO at the time. Initially, the Bundeswehr (German Army) tried to purchase manufacturing rights for the FN FAL from FN, but Belgium rejected the proposition. The Bundeswehr then bought manufacturing of the CETME mod.A, transferred the design to Heckler & Koch, who then began modifying the design, eventually manufacturing the rifle as the G3.
Initial models of the G3 rifle were quite similar to CETME rifles, and even had "CETME" markings on the receivers (until 1961 or so). It is built around Vorgrimlers' roller delayed blowback system. This system employs a two-part bolt with two rollers. The front bolt part (bolt head) is relatively light and has a bolt face with extractor on it. It also has a hollow cavity at the rear, in which an inclined forward end of the rear part of the bolt is inserted. The system features two rollers, inserted from the sides into the bolt head and rested on the inclined forward end of the bolt rear.
Most military G3 rifles feature a green and gray parkerized finish.
When the rifle is fired, the pressure begins to move the cartridge back against the bolt face. The rollers, which are extended into the recesses in the barrel extension, began to move inward into the bolt head, due to inclined shape of the recesses. This movement translates into the faster rearward movement of the heavier bolt body, so at the initial moments of the shot, when pressure in the chamber is still high, the bolt face moves relatively slow.
When the pressure drops to a reasonable level, the rollers disengage the barrel extension completely and the bolt head and the bolt body move backward at the same speed, extracting and ejecting spent case and chambering a fresh cartridge on the way back.
The G3 is built using as many stamped steel parts as possible. The receiver is stamped from sheet steel. The trigger unit housing along with pistol handle frame, also are stamped from steel and hinged to the receiver using the cross-pin in the front of the trigger unit, just behind the magazine housing.
The earliest G3 rifles also featured stamped handguards and CETME-type flip-up rear diopter sights. In the mid-1960s, the initial design was upgraded to the G3A3 and G3A4 configurations. These rifles had ventilated plastic handguards and drum-type rear diopter sights, marked from 100 to 400 meters.
Every G3 rifle can be equipped with detachable bipods and claw-type detachable optic mounts. Long-barreled variants can be fitted with a bayonet or used to launch rifle grenades from the barrel. The folding charging handle is located on the special tube above the barrel, at the left side, and does not reciprocate when the rifle is fired. The selector switch is located above the trigger guard on the left side of the trigger group housing and usually is marked "S - E - F" (Safe - Semi-auto - Full auto). Latest models could have selectors marked with colored icons. It holds 20 rounds in the magazine.
The G3A2 is a G3 with new 'rotating drum' rear sight. The range settings remained the same, but the rear sight was more secure.
The G3A3 was a fixed stock variant of the G3. It featured drum sights, a fixed polymer buttstock, and a polymer handguard. The handguard came in a slim, ventilated variant, and a wide variant. The latter allows for attachment of a bipod.
Late German production G3A3 models were built using new trigger units, integral with restyled pistol grip and trigger guard, made from polymer.
G3A3A1 models feature an ambidextrous selector switch.
The G3A3ZF is an accurized variant with top rails for optics. ZF means Zielfernrohr which means "telescopic sight"
the G3A4 was a collapsible stock variant, with a retractable metallic stock with rubber buttplate, similar to the H&K MP5A3.
Late German production G3A4 models were built using new trigger units, integral with restyled pistol grip and trigger guard, made from polymer.
G3A4A1 models feature an ambidextrous selector switch.
The G3KA4 is a carbine variant of the G3, similar to the G3A4 but with a shortened 12.4-inch barrel. It uses drum sights and a retractable stock.
G3KA4A1 models feature an ambidextrous selector switch.
Danish variant of the G3. It is basically a G3A3 built to Danish Army specifications.
Iranian variant of the G3.
Turkish variant of the G3A3.
The G3A7A1 models are Turkish variants of the G3A4.
The HK91 is a semi-automatic variant of the G3. The '9' stands for semi-automatic export, and the '1' denotes the .308 Winchester chambering. The HK91 has a slightly different trigger group than the G3; instead of the swing-down trigger group that attaches with a push pin, it has a clip-and-pin trigger group that sits on a receiver shelf. The selector switch prevents movement to the AUTO position, and the bolt carrier has a milled slot that will not engage an auto sear catch.
There are no bayonet mounts on these rifles, the grenade launcher rings have been removed from the barrel, it lacks a paddle-style magazine release, and it has a black enamel finish instead of the green and gray parkerizing. Early imports had a blue and gray finish.
- H&K HK33
- H&K HK41
- H&K HK51
- H&K MP5
- FN FAL
- CETMA mod.A
- SIG SG510
- GRAM 63
- FM 1957
- Enfield EM2
- USR M14
- H&K PSG-1