L100A1: G3KA4s of the UK

G3KA4 with SFSG

The G3KA4 is a unique battle rifle that had a brief service life among special operations elements of the UK’s armed forces. Its users included the SAS, SBS, SFSG, CTSFO and Royal Marines. The UK adopted this weapon with the Land Service Number L100A1.

The G3KA4 is 28″ long, weighs 9.7 lbs and uses a more compact 12.4″ barrel instead of the standard 17.7″ barrel. It was generally utilized as a battle rifle but was occasionally pressed into the DMR/Sniper role.

The L100A1 was issued with a B&T extended scope rail (P/N: BT 21174), B&T Tri Rail (very rare, never seen one commercially), Convex HK Telescoping Stock, and Harris Bipods. Variable accessories include KAC/Tango Down/GG&G/Grip Pod vertical foregrips, ARMS/GG&G Harris Bipod mounts, Surefire X200, M952, or very early X300 lights, and 1/2/3 point slings. The LDI DBAL is the only laser seen on the L100A1.

The Army L100A1 was issued with a Trijicon UK Spec TA01 ACOG 99% of the time, (only one has been seen with an Aimpoint M2). The top mounted Shield Red Dot Sights were rarely seen on the G3. There are a few photos showing a PVS4 in use and even one showing a SUSAT optic off of L85 adapted onto a G3KA4.

G3KA4s with PVS4/SUSAT and PEQ2 Lasers.

The Royal Marines Fleet Protection Group’s Maritime Sniper Teams used the G3KA4 with the UK Spec Trijicon 6×48 ACOG, occasionally with a top Mounted RMR. They were all equipped with Grip Pods. They were primarily utilized as aerial gunnery systems and VBSS overwatch rifles. The aerial gunnery rifles were all equipped with B&T brass catchers to prevent brass from entering an engine intake. It is also interesting to note that some of these MST rifles have the newer B&T rail with removable picatinny segments. These MST rifles were also rarely fielded with lasers of any kind.

MST G3KA4 with Grip Pod and New Generation B&T Rail

The G3KA4 was well liked by those who used them, serving until they were replaced by the L129A1 and HK417. The CTSFO G3s will be covered in another post, as they vary wildly from unit to unit. Please contact if you have any questions! More reference photos can be found below.

Cade Johnson

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