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The Barking Dog: Building & Upgrading A G3k In The 21st Century

Retro AR-15s are all the rage, but at the end of the day most of them are simply ARs wearing different dresses. 

Foreign military weapons fall into a seemingly magical category where they’re believed to be ideal by those who haven’t used them, but actually come with some traps and shortfalls. Like the upgraded AUG in RECOIL Issue 65, today we take on the challenge of updating a foreign mini monster, the HK G3k.

The G3 has been used by many countries as their primary service rifle, yet to pop culture, its smaller roller-locked brother, the MP5, is better known, at least here in the United States. The precursor to the G3, the Spanish CETME rifle, was based around the roller-delayed blowback system of the German StG 45(M) and French AME 49. 

In order to accommodate the requirements of a German contract, HK approached CETME to modify their existing design for German production. 

Updates included being chambered in 7.62x51mm instead of 7.62×51 CETME. As with many of HK’s other rifles, Germany wasn’t the only country to produce the G3, with it being manufactured under license by 12 other nations, including Turkey and Greece. All told, the G3 was fielded in some form by over 50 countries, including the British and their renowned SAS through the Troubles. 

During fights with the IRA in Northern Ireland, the SAS reportedly liked the kinetic energy of the 7.62x51mm of the G3 versus the HK33/53 or the MP5, but when working in and around vehicles the gun was less than ideal due to its overall length. HK went back into their shed, grabbed a hacksaw, and cut the G3 barrel down to 12.5 inches. And lo, the G3k was born. They even went so far as to cut some down to submachine gun size with the HK51 and its 9-inch barrel, but it wasn’t fielded to the same extent as the G3k. 


The common theme running through foreign service rifles is the lack of aftermarket support — not just in America. Some models suffer more than others, but the U.S. consumer market seems to drive the modernization of weapons more than military needs or contract verbiage. 

The lower is more modern with Magpul, and the ergos are better as well.

If a firearm becomes popular in America, the aftermarket jumps in to support the weapon. Due to its highly modular design and wide adoption, the G3 hasn’t suffered from a lack of aftermarket parts as much as some others. HK worked to make the G3 as modular as possible, with users having the ability to remove the buttstock and handguard with only a few pins. 

Optic mounting wasn’t integral to the weapon at the time of the initial design but can be handled with Pic rails that clamp onto the upper receiver or having a capable gunsmith weld one on. The trigger falls right in line with many heavy battle rifle triggers — nothing to write home about, and much worse than even average AR-15 aftermarket options. Charging handle placement on the G3 also greatly limits using the top of the handguard for any accessories. 


Working within these limitations, the goal was to build a G3k as a working carbine. Since this project wasn’t modding a factory G3 or HK91, a receiver was ordered from PTR industries along with a ragged German parts kit. 

Joe Stoppiello of Dakota Tactical would be the one to perform the hard labor of putting the rifle itself together, and the multiple conversations we had with companies like Parabellum Combat Systems about the build were incredibly helpful during the decision-making process. 

In terms of parts kits, prices have gone up, and the surplus remnants are worse — it ain’t 2004 anymore. The availability of surplus rifles has been taken for granted, and the currently available G3 parts kits are some of the last ones standing. 

With Joe’s guidance, I procured the parts needed to convert the full-size G3 parts kit to a G3k. For the conversion from a G3 into a full-fledged short-barreled G3k, you need things like the proper cocking tube, cocking piece, barrel, and other assorted small parts. Since this enterprise wouldn’t be a budget build anyway, advice on procuring the right RCM hammer forged barrel to start with was heeded.

With an affection for FDE, when all was said and done, the G3k was finished with the stock HK color RAL8000, aka baby poop.

Stock: Spuhr R-410

The factory stock coupled with the G3k being a 7.62x51mm rifle creates a situation where recoil has sort of a fulcrum point when shouldered. Armalite or AR-based rifles have a straight-back buffer system that pushes directly into the shoulder, whereas the roller-lock HK systems have the more-traditional drop. Hakan Spuhr, one of the mad design geniuses of our industry and founder of Spuhr in Sweden, came up with a new polymer stock for the G3 to alleviate this. It makes the recoil much more like an AR-10. 

The stock is collapsible, with six positions adjusting the length of pull from 12.6 to 15.75 inches. There’s also a cheekpiece that puts the shooter’s eye significantly more in line with modern optics..

Rail: Dakota Tactical MHS-33

The factory plastic handguards don’t leave much in the way of modularity or ability to mount accessories. While there are multiple companies such as B&T and KAC who make Picatinny rails, we went with M-LOK and Dakota Tactical. This simple and slim rail offers M-LOK slots on five sides, is simple to install, and works great.

Trigger: Timney MP5 Two-Stage

If you’ve ever felt the long stiff trigger pull of a stock HK, then this shouldn’t surprise you. While the GI trigger die-hards will talk about how many people have deployed with the factory trigger and done good work, those people also had no choice. The Timney HK trigger is a very nice two-stage with a 2-pound first stage and a 2-pound second stage. The housing is 6061 aluminum with an S7 tool steel hammer. The trigger shoe and disconnector are made of billet A2 tool steel. 

Lower: Magpul SL Grip Module

The G3 and its variants came with several different options for lower receivers. Originally, the idea was for this rifle to have a steel grip, but it was decided for the sake of modernization and better ergonomics to make it more like an AR. And what’s more AR than Magpul? This module offers a grip angle and feel like the grips we all know and love and can be swapped out in a couple of minutes. A Magpul safety selector rounded out the swap.

Optic: Aimpoint CompM4, Unity Tactical FAST COMP, on Dakota welded Pic Rail 

As a 12.5-inch 7.62 with the intent to be portable, the right direction for a sight system was a red dot with magnifier. However, after getting all the parts in place to work with the welded rail, it became evident the magnifier wouldn’t work with the HK rear sight. So red dot only … oh well.

Light: Modlite with Arisaka Mount and Unity Axon SL

The handguard situation on the G3 creates interesting challenges when mounting modern accessories, even with the availability of M-LOK slots. A Modlite with an Arisaka mount attached easily enough but figuring out a switch solution proved difficult. Stoppiello at Dakota Tactical suggested running a reverse Unity Tactical Axon SL button on the rail. This configuration can be hard to wrap your head around, but it works. The M-LOK attachment makes the button wider and more difficult to use any surrounding slots for a hand stop or similar. Cable routing is handled with some Emissary Development cable clips, making for a nice package that’s easily actuated with weak side fingers. 

The Spuhr stock brings the recoil more in line with the bore, making it more manageable.


With the number of rounds most shooters in the states have put through AR rifles, the transition to a new platform can be interesting. The controls might be in another location, the recoil impulse different, and order of operations for things like malfunctions or reloads changed. 

Shooting and training with a G3 or other platform can be frustrating as you work against ingrained training designed for other platforms. Fear not, this is part of the process of learning.

This G3k handles well for a large-frame gun and is about as small as a G3 can be while still being somewhat practical. 

The HK51 and its smaller barrel may look great in pictures, but its actual use is questionable. The gun runs great — and barks out to all those little 5.56mm carbines scattered across the range. 

With the hassle of dealing with the NFA, the loss in velocity in 7.62x51mm with a mere 12.5 inches, and training required to transition from a AR-15/10, would a G3k be a good recommendation as a primary rifle? The answer would most likely be “no,” but we live in one of the last free countries on the planet where you can if you so wish. 

If you’ve always wanted a G3 and the idea of a G3k just excites you, then without a doubt you’ll be happy if you take the plunge. There’s a lot that can be accomplished with this old warhorse. 

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One response to “The Barking Dog: Building & Upgrading A G3k In The 21st Century”

  1. Neal Hutchinson says:

    In 1995 I bought a 1986 converted HK91 to full auto by the Hard Times Armory. Price $1,000. Shooting the weapon shouldered on rock and roll resulted in rounds going over the berm 50 yards away. Disassembly required a trip to the gun store in Cocoa Beach FL for reassembly. Delayed roller blowback is complex. Sold the beast in 1997 for $3,000 to Craig who does the classic gun evaluations on Pawn Stars.

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  • In 1995 I bought a 1986 converted HK91 to full auto by the Hard Times Armory. Price $1,000. Shooting the weapon shouldered on rock and roll resulted in rounds going over the berm 50 yards away. Disassembly required a trip to the gun store in Cocoa Beach FL for reassembly. Delayed roller blowback is complex. Sold the beast in 1997 for $3,000 to Craig who does the classic gun evaluations on Pawn Stars.

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