Explained: Why the Commando Force needs the MCX – its newest new rifle

Personnel from the UK Commando Force have been issued with the Sig Sauer MCX – a new rifle for specialist operations, including counter-terrorism.

The MCX replaces the L119A1 rifles produced by Colt Canada and is designed to complement the Commandos' new general-use weapon, the L403A1, better known as the KS-1.

While at first glance the Sig Sauer MCX may resemble an AR-style platform, the two weapons systems are not the same.

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The MCX uses a short-stroke gas piston system, and weapons expert Matthew Moss, from The Armourer's Bench, explained to BFBS Forces News why this had been chosen by the Royal Marines.

He said: "It's a somewhat subjective topic, but the piston is said to be a little bit more reliable in operation [rather than a direct impingement system].

"So this makes for a more compact package, which of course is really handy when you're clearing confined spaces on board vessels and that kind of thing."

Black theme with .300 Blackout

Another key feature of the MCX platform is its modular nature, giving the Commandos the option of swapping between calibres.

Mr Moss added: "It can chamber the 5.56mm round, which is used with the Army's SA80 platforms, and of course, the new L403.

"But it can also be chambered in .300 Blackout, which means that it can use... reduced velocity rounds like subsonic rounds, which reduce the chances of ricochet within those confined spaces on board ships.

"What the Royal Marines have done with this is that they've quite cleverly decided to pair the .300 Blackout weapons system with a completely different coloured set of accessories.

"So the .300 Blackout weapon systems all have black accessories. So black stock, black optics, black rail, black suppressor.

"So that means that when they're changing the upper receiver or that they're taking a weapon from the armoury, they know that the weapon that they're taking and that the ammunition that they're going to be using in their magazines, which are also colour-coded as well, is the correct calibre for the weapon system.

"So that doesn't lead to any catastrophic failures in the field or accidents."

The need for multiple weapons systems

Mr Moss pointed out that various elements within the UK Commando Force carry out very different roles, hence the requirement for multiple weapons and multiple calibre options.

"While some of the Commando elements are focused on ship-to-shore operations, others are much more focused on maritime interdiction operations," he explained.

Ship-to-ship taskings require a weapons system that's compact. The fact that the MCX mix doesn't have a fixed stock means it can be equipped with a folding stock.

Size matters

"The Royal Marines actually posted a good video illustrating this feature, showing a Royal Marines Commando firing one of the weapons at the range with the stock both folded and deployed.

"And in confined spaces that's a real advantage to have the ability to fold that stock, especially if you're going to transition to a sidearm.

"When it's a really confined space and you need to draw a pistol, having the fact that you can fold that stock away and stow the weapon to your rear quarter and know that that compact-sized weapon isn't going to be banging around and catching on other bulkheads and that kind of thing is a real plus.

"So we have to think about this in terms of it being a special operations force role-specific weapon system."