Is Piston or DI Better For Shooting 5.56 Suppressed?

Test setup and suppressed 5.56 goal

The video examines whether a piston or direct impingement system runs cleaner when shooting 5.56 suppressed. Both systems are described as proven and reliable, but the focus is on how dirty each gets under back-pressure-heavy suppression rather than with flow-through silencers. The test uses a SureFire RC2 suppressor wrapped in a Liberty Defense suppressor wrap. Clint plans to fire roughly 100 rounds through each upper and then inspect carbon buildup. This segment also sets up a future collaboration with Golden Web, where an LMT piston upper and an LMT direct impingement upper will be shot to failure to see which operating system ultimately lasts longer.

Clean LMT uppers and operating system overview

The rifles used are LMT 5.56 setups with similar barrel lengths, around 14.5 inches. One is a complete LMT R20 Estonian reference rifle with a piston system, and the other is an LMT direct impingement upper on a separate lower. Both guns start the test very clean. The DI upper uses a nickel boron coated bolt carrier group with a light coat of oil and only minor staining, not carbon. Chambers on both rifles have been thoroughly cleaned. Clint explains how direct impingement routes gas from the gas block through a gas tube into the gas key and bolt carrier group, where gas drives the action and vents out the side. In contrast, the piston system vents most gas at the gas block and uses an operating rod to strike the carrier, so gas does not travel through the bolt carrier group and should, in theory, keep the system cleaner.

Running 100 suppressed rounds through each upper

Instead of simple mag dumps, the rounds are used for drills to get some training value while still putting about 100 rounds through each upper. Both uppers are run with the SureFire RC2 suppressor and Liberty Defense suppressor wrap installed the entire time. After the shooting, the suppressor and wrap are extremely hot, and there is a noticeable smell from the heat and gas, but the wrap holds up without apparent issues. Across the roughly 200 total rounds fired through the suppressor, there are no malfunctions or reliability problems with either the piston or direct impingement setup. The rifles are then set aside to cool before disassembly and inspection to evaluate how much carbon and fouling accumulated in each operating system when shot suppressed.

Inspecting carbon buildup on the LMT piston R20

Once cooled, the LMT R20 piston rifle is separated into upper and lower for inspection. The lower receiver shows significant fouling: the buffer is described as filthy, and carbon buildup is clearly visible on the hammer and inside the lower. A clean paper towel quickly turns dark when wiped on the hammer and buffer area, indicating substantial carbon accumulation despite the piston design. The upper receiver also shows noticeable fouling. Wiping inside the upper and around the buffer area produces a heavily soiled paper towel, and the charging handle, which started clean, is now visibly dirty. This section highlights that even with a piston system, suppressed fire with the RC2 still drives a considerable amount of gas and carbon back into the action, contradicting the expectation that the piston gun would remain almost clean after only 100 rounds.

Inspecting carbon buildup on the LMT DI upper

After cleaning his hands with D-Lead style wipes to remove lead and carbon, Clint moves to the LMT direct impingement upper mounted on a Mk18-style lower. Using a fresh paper towel, he inspects the lower receiver and finds it very dirty, with the H buffer and surrounding area heavily coated in carbon, similar to or worse than the piston gun. The hammer shows clear carbon buildup when wiped, and the interior threads where the buffer sits are caked with fouling. The nickel boron bolt carrier group, which was shiny and clean before, now appears dark, almost like a parkerized carrier, due to carbon deposited where gas vents from the carrier. The charging handle and upper receiver interior are also heavily fouled. While the nickel boron finish allows carbon to wipe off relatively easily, the DI system is clearly dirtier overall after 100 suppressed rounds.

Comparing piston vs DI trade-offs and next test

The comparison shows that the direct impingement upper is noticeably dirtier than the piston R20 after the same amount of suppressed fire, but the difference is not dramatic. Both systems accumulate significant carbon when using a traditional suppressor like the SureFire RC2. Clint notes that DI rifles tend to be lighter and more accurate because only a gas block and gas tube are attached to the barrel, while piston systems add more moving parts on the barrel, increasing weight and potentially reducing accuracy. Piston guns are expected to run cleaner but are often heavier and more expensive. Despite getting dirty, the DI system still runs reliably. The video closes by questioning whether piston rifles are truly better overall and points ahead to the planned Golden Web collaboration, where an LMT piston upper and an LMT DI upper will be shot until failure to compare long-term performance.