Bolt, a company known for makeing AEGs with a special recoil mechanism, recently released their latest version of the “B.R.S.S.” Recoil system and put it into a full sized battle rifle – the M16A4.

When I first got the Bolt M16A4 B.R.S.S. Heavy I didn’t know what to expect at all. I’ve never been a big fan of the AR platform and certainly no fan of recoil shock AEGs either as those systems usually are more for the look than actually work. The Bolt M16A4 is different as it generates far more recoil energy as one would expect from an AEG.

I’ve read some of the recent reviews of the M16A4 but they all where missing the technical details of the gun and its recoil mechanism. I’m going to focus on the technical details and will explain the recoil mechanism and take a look inside the gearbox.

Let’s be honest: it’s an M16. Everyone knows how a M16 feels like, shoots or handles. It’s nothing new to most players. The BRSS Heavy system although is something new. And yes, it really kicks. I won’t lie, I would compare its recoil to the recoil of a .22lr rifle.



The build quality of the M16A4 is great. The paint/coating is more on the shinier side but well done. The colors of the various metal parts don’t match the color of the receiver, which is a bit of a downer as it lets the gun look a bit cheap-ish.

The markings are laser engraved and look nice. The lower receiver has a sticker with some sort of QR code on it similar to the real steal M16A4 issued in the US Army (IUID code). The “B4A1” markings are also a downer as it seems that Bolt didn’t create a unique laser template for the M16A4 and instead used the template from their M4s.

The M16A4 also comes with two rubber RIS covers and a barrel extension. Yes, a barrel extension. I have no idea why Bolt did this. Due to the removable barrel extension, the inner barrel is also shorter so that it doesn’t stick out. In my opinion, one of the biggest benefits of a long rifle like the M16A4 is that it can utilize a long barrel thus gaining range an accuracy in the field.

You basically get the barrel length of a M4 in a heavier and bulkier package. The positive side of having the possibility of shortening the rifle is that you can customize the rifle better and/or make it more compact for CQB games and other scenarios. I would have preferred the longer inner barrel as it would have made the M16A4 even more accurate.

Hop-Up & Inner Barrel

The inner barrel is made out of aluminum and has a diameter of, obviously, 6.0mm. I’m not sure if this is a true 6.00mm barrel or if Bolt have just omitted the last figure of the diameter measurement for marketing reasons. The rifle shoots very accurate and far for such a short barrel. The hop-up is made out of polymer and has a rotating dial which works very well.

The Recoil Mechanism

Ok, let’s dig deeper into the rabbit hole and take a look under the hood. The Bolt M16A4 disassembles like any other M4 or M16 AEG. The first thing that looks unfamiliar is the fake bolt and its recoil mechanism.

The fake bolt has a hook that the piston catches while moving back and the fake bolt cycle back. The mechanism disassembles very easily by pushing the rod back and removing it from the shell.

This is where the magic is happening – the stock. The stock has a plastic end cap with a battery port which is made out of plastic and feels very cheap. I couldn’t close the battery door every time and sometimes the door just popped open trough the recoil. It’s also very hard to get the door open when you don’t have a knife around or have long fingernails.

The stock tube is longer and thicker than your normal M4 stock tube. Inside the tube is a metal weight and two springs. The recoil weight is connected to the piston trough a push rod. The rod itself is made out of two parts and dampens itself with an air cushion inside.

The recoil works well and I can confidently say that this is the best recoil action on an AEG I have ever experienced. The kick is quite hard, not as hard as a GBBR kick though. Shooting full-auto requires you to hold the M16A4 tight – the muzzle moves arround quite a bit.

I took the Bolt M16A4 with me for a game at the Airsoft Area Ginzling and handed it to a few other players. The first time shooting the M16A4 made everyone giggle like a little child and people liked the recoil a lot. Shooting it on full-auto was everyone’s favorite.


The motor is a high-torque one with strong magnets and a lot of power. The recoil mechanism requires a decent amount of power to operate. The pistol grip has a metal plate inserted at the very bottom which may act as a reenforcement.

The gearbox looks unspectacular and reminds me of the Tokyo Marui gearboxes. The top section looks different than your typical V2 shell due to the fake bolt and its mechanism.

The back of the shell where the spring guide sits is open so that the push rod can go trough.

The inside of the gearbox is simple but effective. The Bolt M16A4 uses bushings instead of bearings. A good choice when considering the force that acts on the gears when pushing the recoil weight back. The gearset is well made and feels very solid.

The piston is made out of a slightly thicker aluminum and has a metal insert inside where the push rod pushes against the piston head. This is one of the sturdiest pistons I’ve seen in a while. The piston head is made out of aluminum and is ventilated. The cylinder is a standard brass M4 type. The cylinder head is made out of aluminum too and has two o-rings for a better sealing. The nozzle is made out of polymer and has an o-ring on the inside.

The tolerances inside the gearbox are very tight. The compression of the piston head is perfect. There is no air leak, even when the nozzle is on the very end of the cylinder head. Well done, Bolt! There’s no need for tuning parts here.

Final Words

The 3500g heavy Bolt M16A4 delivers around 382FPS and a rate of fire of roughly 700RPM with a 7.4V LiPo battery. The range and accuracy are very good even with the short barrel thanks to the great gearbox and the tight tolerances.

The gun is fun to play with and offers a quite unique experience. The missing markings and the color mismatches are a little downer as is the short inner barrel but the Bolt M16A4 is a perfect gun for those wanting a strong recoil mechanism without sacrificing the benefits of the AEG system. The AR platform is also perfect for customization as there are a ton of third party parts available.

I can’t tell you the retail price or where to buy the rifle as there are almost no shops that have it in stock or are selling it. One of the only shops I could find is Airsoft World which sells the M16A4 for around 500USD (in Europe).

Thanks to Bolt Airsoft for letting us test the rifle.