Over the last few years, one of the most interesting accessories developed for Heckler & Koch’s venerable roller-delayed weapons is the Spuhr Stock. Developed by Swedish firearms inventor and toolmaker Håkan Spuhr, the Spuhr Stock offers a more comfortable and adjustable stock in place of the factory butt used on Heckler & Koch’s classic 7.62x51mm battle rifle.

A West German Army machine gun team with a 7.62x51mm MG3 and a G3 rifle on exercise c.1960 (US Army)

The story of the Spuhr G3 Stock is definitely one of iteration, with Håkan making a number of improvements to develop the answer to a fundamental issue with the rifle. In a recent post on Facebook, Håkan said “I never liked the G3 it always been awkward to handle, never really thought about why but it’s an ergonomical disaster!” He’s right. The G3’s stock was designed at a time when adjustability was not a factor. The G3’s plastic buttstock followed the same dimensions as the original wooden stock and doesn’t allow a length of pull adjustment.

An early production Rheinmetall G3 disassembled (Matthew Moss)

Spuhr note that the G3’s stock is 75mm/3in longer than the contemporary M16A2’s stock. The shape of the stock is dictated by the position and height of the low-profile Heckler & Koch diopter sights. The drop in the comb of the G3’s stock also means the rifle lacks the benefits of in-line recoil to improve controllability. Håkan refers to the drop in the stock’s comb as the ‘cheekbone cruncher’, noting that it often strikes the face when firing from the prone position.

Last year Spuhr shared a video in which Håkan explains the problems with the G3’s stock in detail:

In 2012, Håkan began experimenting with ways of improving the G3’s stock. He explains that he had a wooden stock on his own G3-pattern rifle and simply put it “in the bandsaw, shortened it 5-7 cm and cut cheekpiece off”. He then glued on a wooden piece to the top of the stock and sanded it down. After a trip to the range, he felt he was onto something, feeling that the rifle handled much better. While the rifle handled better, the rise in the height of the cheek position did render the original Heckler & Koch sights useless. However, with a top-mounted Picatinny rail, an optic could be mounted for testing.

Spuhr’s original proof of concept prototype with wooden stock (Håkan Spuhr)

After the range trip with the homemade adapted stock, he then machined an adapter that allowed him to fit a standard AR-15 buffer tube, this allowed him to mount a Magpul CTR adjustable AR-15 stock. The buffer tube had to be installed high in line with the top of the rifle. This meant that there was no longer room for the G3’s original buffer spring, which normally extended back into the stock. Håkan overcame this problem by making a simple rubber buffer which could be placed inside the new adapter.

The adapter developed to allow an AR-15 pattern stock to be added (Håkan Spuhr)

After several years of development and demonstrating the improvement the new stock made to the G3’s handling, the Swedish Försvarsmakten (defense forces) became interested in the design. They subsequently launched a tender to upgrade their Ak 4 (G3) rifles, which are widely used by the Swedish Hemvärnet (Home Guard). The Swedish tender required that the rifle’s original buffer should be used which forced a further redesign with Spuhr moving from an adapter to an all-new proprietary stock design.

The CAD render for the new stock (Håkan Spuhr)

Further development and the use of 3D printed prototyping allowed Spuhr to develop a completely new stock design with adjustable length of pull (12.5in to 15.5in, with six positions) and a cheek comb height in line with the top of the rifle’s receiver. The buffer issue was addressed by lowering the main tube of the stock in line with the buffer and adding an adjustable cheekpiece on top. The Spuhr Stock won the contract and was also awarded a further order in October 2019.

An 3D printed prototype of the stock (Håkan Spuhr)

The production Spuhr G3 stock (Håkan Spuhr)

In June 2019, the Portuguese Navy and Marines selected the stock, along with other Spuhr upgrades developed for the G3, to upgrade their rifles. In October 2019, the German Bundespolizei selected Spuhr’s MP5 stock to upgrade 6,000 of their MP5 carbines. Spuhr have also recently developed a prototype folding stock variant for the Heckler & Koch MP5, HK33 and HK53.

Portuguese marines during an exercise at REP-MUS-19

Spuhr’s shorter, adjustable stock undoubtedly makes the Heckler & Koch roller-delayed weapons easier to manipulate and control their recoil. It also prevents issues with stacking more length of pull when wearing load bearing gear and body armour. The stock system has arguably extended the service life and usefulness of the G3 and other Heckler & Koch weapons that use the same type of stock.