Words: Rich Norman

Thanks to a very good friend of the blog, I was presented with the golden opportunity of acquiring some barely used RS Colt Canada parts for my HAO L119A2 PTW build:

  1. Receiver Extension Nut
  2. Receiver Extension – 6 Position
  3. Ambi Magazine Catch Assembly
  4. Ambi Charging Handle Assembly

Anyone who has followed my builds over the years will know that I try to use as many RS parts as I can, so it should come as no surprise that I jumped at the chance and am very grateful for the opportunity to furnish my A2 with legit parts. These are not easy to source components.

One thing I really like about the PTW is that many RS parts are a drop in fit. It’s this 1:1 compatibility which attracted me to the platform in the first place, along with all the other benefits.

I’m impressed with the quality of these Colt Canada parts and I’m sure that the company’s attention to detail is just one of the reasons their products are trusted by Tier 1 operators like the SAS and SBS; not to mention those in Canada, Norway, and other NATO countries.

Below I’ll compare the Colt Canada parts to some from Colt USA that I’ve accumulated, plus other alternates. Don’t think of the Colt USA items as definitive, however. As far as I know they are not ‘Government’ AR items, just components that were easily available from Brownells UK.

1. Receiver Extension Nut (CF62357)

Colt Canada’s Receiver Extension Nut is a classic design, which has largely been replaced in the AR market by the ubiquitous ‘castle nut’.

Prior to the castle nut, this style was used on all US manufactured Colt AR15s between 1965 and 1992 (according to Nordic Marksman) and exhibits a cylindrical torquing notch. The more modern castle nut, on the other hand, exhibits characteristic turret-like torquing notches.

Note that compared to my Colt USA AR6721 castle nut, the Colt Canada item is shorter. It also has four staking notches – not three. This is an improvement, as it gives more opportunities to stake the item.

According to a friend of the blog with a professional background in the Canadian firearms industry, Colt Canada has been supplying nuts with four staking notches since around 2010. However, they continue to supply three and four notch variants and do not seem to differentiate between them, because they exhibit the same part number.

But what is staking?

Staking is a process by which an interference fit is created between two components, with a whack from a hammer. Material is displaced by the blow – normally via a centre punch. The displaced material creates a tongue which intersects with a notch on the item being staked, thus keeping the two components captive.

Again, according to my professional contact, Colt Canada receiver extension nuts are staked at the factory. That’s an important point, because I’m building a replica L119A2.


The pic above isn’t an L119A2 but it is a Colt Canada rifle, as depicted in the Vickers Guide. Thanks to Michael for pointing it out.


2. Receiver Extension – 6 Position (07922C-5)

Commonly known as a buffer tube, Colt Canada’s Receiver Extension – 6 Position differs in a number of ways from the Colt USA AR6721 item. The most obvious difference being the colour, which is a lighter grey; although not as light as my LMT buffer tube, as can be seen in the final pic below.

The Colt Canada item is also smooth (a close look at the Colt USA item reveals pitting) and has a more attractive finish.

3. Ambi Magazine Catch Assembly (11495C-1)

An ambidextrous mag catch in the Norgon style; Colt Canada’s Ambi Catch Assembly is made in Canada under license from Norgon themselves.

The item is stamped with Colt Canada’s CAGE code “2C085”, and the “.1” as also seen on Canadian Forces C7/C8 rifles.

These markings are, of course, present on the L119A2 and it’s a nice little detail that the Norgon and True North Arms ambis don’t feature. If I was keeping the True North Arms item – or I had the Norgon – I’d get the 1. engraved.

The True North Arms ambi (review here) is shown below for comparison. Note the Colt Canada item’s aggressive grip profile, compared to the True North Arms version.

4. Ambi Charging Handle Assembly (9978334-1)

Commonly known in the British Army as a “cocking handle”, the Colt Canada Ambi Charging Handle is forged from 7075 aluminium which is, according to Nordic Marksman, machined and inspected to Canadian Department of National Defence specifications.

The extended tactical latch is purposed for ambidextrous operation and is heat treated and phosphate coated.

Shown here with my Colt USA AR15A4 charging handle – which features HAO’s ambi latch – the Colt Canada item is almost the spitting image, but exhibits a satin black finish which looks and feels really high quality.

It’s pretty cool that the Colt Canada item seems made for HAO’s L119A2 IUR. The Colt USA item is a bit sticky on pull back; almost like it’s a hair too big. Hats off to HAO for getting the IUR’s dimensions spot on for this application.

Also of note is the butter smooth operation of the Colt Canada ambi latch. It is quite unlike any latch action I’ve come across before in a charging handle.

Read part 1 of the series, here.

Catch up on the full HAO IUR series here.

More articles relating to the L119A2:

  • The original L119A2 primer, here
  • GG&G AR15 vertical fore-grip in use here
  • Magpul QDM and ASAP QD in use here
  • 15.7″ L119A2 upper in use here
  • Surefire FA556SA Suppressor here
  • GG&G Aimpoint T1 mount in use here
  • Magpul MS3 sling in use here
  • Magpul ACS stock in use here
  • Colt Canada parts – as used on the L119A2 – here
  • Manta Very Low Profile Rail Covers as used on the L119A2 here
  • UKSF Newcastle raid pics part 1
  • UKSF Newcastle raid pics part 2
  • UKSF Nairobi Kenya incident L119A2 parts breakdown here
  • UKSF Belize ‘Jungle Set-up’ L119A2 parts breakdown here
  • Confirmation bias (and the HSP Thorntail offset light mount) here
  • UKSF Ecosystem: S&S Precision Sling Clip – Old Gen – here
  • Inforce WML-type lights in use here

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Obi Wan Nairobi patch from Platatac