Siege Suppressors ROC556L Review [VIDEO]

While many suppressor manufacturers run toward 3D printing, Siege Suppressors took a different route in creating an entirely novel internal geometry and gas flow system that delivers modern performance with traditional manufacturing processes and materials. The result is fantastic.

That is what Siege calls their Linear Diffuser Array. It’s obviously very different from your typical cone-style baffles. In fact, it has no “baffles” as we typically think of them.

As you can see in the slow motion video from that Lexan-bodied suppressor, the Linear Diffuser Array appears very effective at slowing down the combustion gases by providing a complicated exit path. Delaying the gas allows it to cool, allows pressure to drop, and results in the sound suppression we look for from a firearm silencer.

Siege touts that the contiguous bore of the ROC556 reduces baffle erosion as compared to a traditional silencer:

The contiguous bore is a design feature that offers increased erosion resistance compared to conventional designs due to the flow characteristics of propellant gasses and unburned gunpowder through the suppressor. Because there are no angular features and no baffles used in the internal construction of the suppressor, the propellant gasses and unburned gunpowder have no angular barriers to react against and therefore erode over time.

There is precedent for this concept, which can be seen in the ROC556’s only actual baffle, its blast baffle. Modern suppressor design has moved away from using blast baffles with a steep cone with a thin wall around the bore and sharp edges to a design more like what’s seen above; a shallow cone with a thick or rounded wall around the bore and gas ports around the circumference to encourage gas and pressure to travel along the periphery instead of through the bore.

After the blast baffle it switches to the Linear Diffuser Array, which appears to stagger and otherwise offset small expansion chambers, forcing the gas to constantly change directions as it attempts to travel through the suppressor.

Manufactured from machined Inconel and precipitation hardened stainless steel (usually this means 17-4 PH but I don’t believe Siege specifies on their site), even with a traditional baffle design the ROC would be considered a hard-use suppressor. Given the modern, heavy-duty design of the blast baffle and Siege Suppressor’s claims about the bore design of the diffuser array being less prone to erosion, it’s no wonder Siege rates both the ROC556L and ROC556K (the shorter version) for heavy full-auto use without any barrel length restrictions.

Another claimed benefit of Siege’s Linear Diffuser Array is reduced back pressure. They consider the ROC cans to be “high flow” such that they won’t noticeably increase gas blowback into the firearm’s action or the shooter’s face, and they won’t affect the cycling of the firearm (increased back pressure can cause a gas-operated gun to cycle too hard and/or fast). The very cool looking front cap certainly nods toward the high flow design and also incorporates flash hiding features.

In the box, a Siege Suppressors ROC556 comes either as seen above with direct thread mount and two tools or with a QA mount and a Plan B-compatible, QA muzzle brake.

Should you want to run a different mounting system, Siege’s ROC silencers are HUB threaded at their base. In 2025 it’s a smart decision to use this “universal” HUB 1.375×24 thread size.

Out on the range at Copperhead Creek Shooting Club we slapped the Siege ROC556L on a Stag Arms Stag 15, which is an excellent rifle but is, at the same time, a totally “standard” AR-15 in its layout and operation. This bad boy has a mid-length gas system with a non-adjustable gas block that provides plenty of gas for the system to work with and it has a standard weight bolt carrier group, buffer, and buffer spring.

This is about as quiet as I’ve heard any 223/5.56 AR-15. The suppressor is extremely impressive at sound mitigation. With hearing protection on, the loudest noise we could hear was the buffer spring’s scratchy, springy, annoying sounds as it compressed and rebounded inside the receiver extension. Without hearing protection, the rifle’s bolt carrier and the supersonic crack of the projectile traveling downrange became the loudest sounds. The actual gunshot itself was shockingly quiet.

Additionally, we noticed almost no gas blowback whatsoever and near zero visible jets of gas out from the ejection port. This is not the norm with an AR-15 of this sort when equipped with any traditional suppressor. The rifle still felt smooth and properly-tuned and there was no indication that the buffer weight was bottoming out inside of the receiver extension (buffer tube). Suffice it to say that, yes, the ROC556 absolutely appears to be a high flow suppressor that has very little effect on gas back pressure or blowback.

Typically a high flow suppressor like this, which vents more of the gas out through the muzzle and less back through the action, also reduces sound volume levels at the shooter’s ear. This is certainly in keeping with our experience on the range with the ROC556. At the same time, it also sounded much quieter for everyone else on the range compared to many of the other high flow suppressors on the market. Typically there’s some trade-off between reducing sound at the shooter’s ear and increasing downrange sound, but in the case of the ROC556L it was all-around one of the very quietest suppressed AR-15 setups we’ve shot.

After this extremely impressive showing on the range where all three of us agreed the ROC performed as well as or perhaps better than any other 5.56 suppressor we’ve shot, I’m left with only one aspect of the suppressor that isn’t ideal: at 18 ounces it’s a bit on the heavy side. Yes, it’s a super hard-use, extra durable suppressor and that warrants some additional weight. Yes, the K (short) version weighs 14.5 ounces, which is a more competitive spec these days, but it’s fair to expect it to be a little louder than the L reviewed here (we haven’t yet tested the K flavor). In no way do I think 18 ounces is disqualifying or “too heavy” or anything, but in my quest to have some nitpick or gripe or “downside” in every product review, the stellar performance of the ROC556L has left me with nothing else but to say that I’d prefer it was lighter.

GREAT suppressor.

Specifications: Siege Suppressors ROC556L

Caliber: 5.56mm
Length with mount: 7.70”
Length w/o mount: 7.45″
Diameter: 1.5”
Weight: 18.06 oz
Materials: Precipitation Hardening SS & Inconel Linear Diffuser Array
Finish: Nitride
Full Auto Rated No Barrel Length Restrictions
MSRP: $1,049 (available at a great price via Silencer Shop)