Hera Arms - TRIARII Pistol to Carbine Conversion REVIEW

Hera Arms - TRIARII Pistol to Carbine Conversion REVIEW

The BUY USED GUNS Team review the Hera Arms – TRIARII Pistol to Carbine Stock System


Many of you are probably wondering straight away, what is it exactly? We will get this out of the way first so you have a better understanding of the product and this review.

The Hera Arms - TRIARII is an aluminium stock or chassis that your pistol ‘slides’ or ‘sits’ inside, transforming your pistol into the feel and look of a small carbine. It does not increase barrel length, magazine capacity or change the way the pistol operates in any way. When you shoot using the TRIARII you are still only firing a semi-automatic pistol.

WHY would you want to do this? Well shooting a pistol inside the stock increases accuracy and stability whilst firing your pistol. It also allows for alot of accessories and attachments. This product would certainly have military/law enforcement applications however we won't cover those topics in this review.


What do I get for my money?
The stock system as it comes is pretty useless by itself, as shown in the below photo. You need to install accessories to make if functional, namely a butt stock and sights. Sights are the bare minimum required to actually use the stock to some degree of effectiveness (plus your pistol). Otherwise you would just be looking at a bare rail, (not very effective for aiming).



You could use the stock without installing a receiver extension and butt stock but again, you wouldn’t be utilising the stock system to its full potential. The stock is made from ‘aircraft grade’ aluminium. The Buy Used Guns Team were very impressed with the overall quality of the product. We could not fault the quality in anyway. Typical German engineering.

After you decide which pistol you want the TRIARII Stock System to use with, all you need to do is choose the colour, either black or tan. Please see below a list of pistols the stock is made for, this was sourced directly from the Hera Arms website;

  • SIG 226 (Picatinny Rail)
  • SIG 2022 (European Model)
  • Glock 17/19/20/21/22/23/31/32/34/35
  • CZ SP01
  • HK P30
  • HK P30L
  • Walther P99 (Gen.2 +)
  • Walther PPQ
  • S&W M&P9

Our TRIARII stock is for Gen4 Glock 17’s, 22’s and 31’s, (9mm, 40S&W and 357sig). You may notice we are actually using a Gen3 Glock 17 in our TRIARII. We found the Gen3 Glock 17 to function flawlessly in the TRIARII designed for Gen4 Glocks. This may be due to very little difference between Gen3 and Gen4 Glocks.




The stock system is very simplistic in its function. The pistol is held within the stock via the front accessory rail on your pistol and a small bracket at the rear of the stock specifically designed to sit against the rear of your make and model of pistol. There is a side ‘charging handle’ which allows you to move your pistols' slide back and forth as required.

Why would you want to attach a large aluminium chassis to your pistol? There are a few reasons. It adds A LOT of rail allowing for A LOT of accessories. There is a full length rail running along the top of the stock along with 3 shorter rails on the sides and bottom. The other reason being you can attach a receiver extension also known as a buffer tube to the rear of the stock allowing you to mount many different adjustable butt stocks. The stock does come with a ‘plug’ and sling attachment, should you wish to use the chassis without a butt stock installed. The rear stock can also be adjusted to sit on an angle as per the below photo. This is done by simply loosening one bolt.


You can see on our TRIARII Stock System we have installed numerous accessories, namely front and rear flip up sights, red dot scope, front vertical grip, rail covers and an adjustable butt stock.


The accessories you add are really what transforms your pistol into a carbine like firearm. Hera Arms have made a smart move in supplying the stock system by itself. This allows the end user to truly customise the stock to their shooting style and tastes. Hera Arms state you can install a pistol into this stock system within 4 seconds. With a bit of practise this is not impossible. We recommend installing your pistol into the stock UNLOADED. This will prevent any mishaps. Loading and unloading your pistol whilst installed in the stock is quick and easy, utilising the side charging handle.


Step 1: Twist the locking knob to unlock and slide the front of the stock forwards

Step 2: Slide your pistol into the stock (there is a slot designed specifically for your pistols accessory rail)

Step 3: Slide the stock and pistol backwards closing the locking knob and you're ready to go!


Shooting the TRIARII

There is no doubt about it, shooting pistols using this stock system is a lot of fun. We found many of the benefical attributes of shooting a carbine/rifle carry over to the TRIARII. You can expect a more stable shooting platform, less muzzle flip, increased overall accuracy (due to stability of the pistol) and reduced recoil. Although the recoil is aborbed mostly through the stock into your shoulder. We ran a simple accuracy test shooting our Glock with and without the TRIARII. Results are as per the below photos and as you can see, groups were tighter using the TRIARII, (with the exception of a couple flyers).




You can install/remove your pistol in seconds with no modifications to your pistol at all. Obviously you need to utilise the front accessory rail on your pistol and the small gap between your pistols slide and the top of the stock will probably limit your pistol to open sights only.

The only downside to shooting the stock is the build-up of carbon and fouling inside the fore end of the stock. This is unavoidable due to the design of the stock and can be difficult to clean due to the tight space. Luckily with the chassis being aluminium you won’t ever have to worry about rust.

During the thousand or so rounds we have fired using the TRIARII stock we did not expereince ANY malfunctions. The design of the stock is great in that it does not interfer with the operation of the pistol in anyway. It simply 'holds' the pistol via the front accessory rail and rear of the reciever.





If you are after a pistol stock/chassis system to have some fun with you can’t go wrong with the Hera Arms TRIARII. The quality is second to none, along with the ease of use and ability to accessorise.

You will need to check the legality of these stocks within your state/territory before going out and purchasing one. Many issues come to mind such as pistol maximum lengths and possible military appearances.

If you can legally own one then the Buy Used Guns Team highly recommend you do so! There are not many places you can purchase these stocks within Australia. The cheapest the Buy Used Guns Team have seen them has been approx. $600AUD for the bare stock system. The price will no doubt be closer to $1k once you add decent quality accessories and sights.

Don’t forget the stock system is limited to specific pistol models, you can’t use any pistol with any TRIARII stock.




  • Fun! You are transforming your pistol into the look, feel and somewhat operation of a small carbine
  • Ease of use
  • Quality
  • Ability to accessorise
  • Lightweight



  • Expensive (In Australia at least)
  • May not be legal in your state/territory
  • Cleaning inside the fore-end can be difficult


Specifications (as measured by the Buy Used Guns Team using our TRIARII Stock with the rear plug/sling attachment and NO accessories/pistol installed)

  • Weight - 1088 grams
  • Length - 447mm
  • Height - 72mm
  • Width - 81mm (including the charging handle)


If you have any questions about the Hera Arms TRIARII Stock System don’t hesitate to send us a message! We also love feedback on our reviews.


Check out the TRIARII Stock System on the Hera Arms website;




Great review guys. Keep it up!

Don 10-23-2014 09:14PM

I thought these would have to be illegal in our country? They look like they are too much fun.

Ken 03-27-2015 08:39AM

You make a conversion kit for Walther P99 QA

Batin, Marlon 07-23-2015 10:37AM

Would you be so kind and tell me what is the maximum and minimum length of pull of tirarii (with the standard AR15 stock on the buffer tube)

Best regards

Bartek 08-07-2015 06:52AM

Where do I buy this. I like it better than the kpos and roni

Frank motta 09-28-2015 02:46PM

Bartek - apologies for late reply, we don't have the kit anymore to measure sorry!

Frank Motta - Last time we checked Cleaver Firearms in Brisbane, QLD stocked them.

Dee 09-28-2015 06:34PM

Hi guys, will a glock 17 long fit into one of these. It looks like it slides into the pic rail at the bottom which a glock 17 long doesn't have.

Jessie Chisholm 06-01-2017 09:42AM


No don't think it will


Matt 06-01-2017 03:30PM

Hi guys great review few years old now, but wondering do I need a permit for the chassis ? Or can I just come in and grab one ?

John 01-11-2018 03:51PM

Hi John

We can only speak for QLD, they do not require a licence to buy or own, they are simply a piece of aluminium, just a firearm accessory.

Buy Used Guns

Admin 01-11-2018 04:51PM
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