In 2017, gun maker Sig Sauer landed a five-year, $48 million contract with U.S. Special Operations Command to upgrade operators’ M4A1 carbines with integrally suppressed upper receivers, an aggressive move toward a future warfighting concept that some have called the “stealth infantry.”The idea: to radically reduce the sound signature of friendly troops by suppressing every weapon on a battlefield.

The contract also plunged the company into engagement with an emerging area of concern: the health dangers of toxic gases and particles blasted back into the shooter’s face when firing a suppressed weapon.

While the full extent of the risks is still being understood, SOCOM made it clear to Sig at the time of the contract that it wanted to cut down on toxicity, setting a standard that seemed unreachable.

“The requirement at the time was that they wanted a suppressed upper receiver group that produced less toxicity than an unsuppressed M4,” Josh Shoemaker, product manager for defense systems at Sig, told Military Times. “At the time the industry was all like, ‘That’s not physically possible.’ It was really a set of requirements that was defying everybody’s understanding of suppressors.”In the years that followed, Sig would come under fire multiple times for tests that showed various suppressed weapons had too much toxic blowback. But through lengthy development and the introduction of advanced manufacturing, Shoemaker said, the company reached the ability to reduce 70% of toxic gas blowback in a suppressor.

But there’s a tradeoff, he added. Suppressors can excel at reducing noise, flash or blowback, but not all three at once. One solution the company is now proposing would offer specialized suppressors that maximize blowback reduction for training and signature masking for combat.

The idea, Shoemaker said, is that troops are most at risk from toxic gas exposure when shooting in enclosed spaces and over long periods in the same area, both of which are more likely to happen in training. On top of that, he said, training accounts for the vast majority of the rounds a soldier will ever fire.

“The Army already has this principle where they have training ammunition and go-to-war ammunition. When they go to war, they’re using a different projectile and different ammunition than they are when they’re training,” Shoemaker said. “They do this with their body armor, with their uniforms — their uniforms, when they’re training, are not all flame retardant. … Why wouldn’t we do that same thing with the suppressors?”Early in its 10-year production contract to design the Army’s next rifle and light machine gun — a program known as Next Generation Squad Weapon — military testing officials cited concerns about how much toxic back-blast the suppressed weapons were producing. The result was a delay that pushed fielding from late 2023 into 2024.

And these problems continued to be reported as recently as last year. The Pentagon’s weapons testing branch noted in its Fiscal Year 2025 annual report that soldiers in an operational assessment “reported negative physiological effects caused by the noxious off-gassing from their weapons, as well as concerns about the extreme heat from the weapons’ suppressors after firing.”Shoemaker said that some of this feedback was expected when comparing the previous standard rifle, an unsuppressed M4, to the new M7, which has a larger round and a more powerful discharge. But he added that the company was listening to soldiers and “actively working” to address concerns.

“Toxic fumes [are] still a very new thing, right?”Shoemaker said. “When you have a very narrow audience that you’ve been providing these products to for years, you don’t get the same feedback that you do when you’re providing to a much wider audience.”Behind the scenes, according to Shoemaker, Sig has been close to the forefront of fume-reduction technology. The company uses a 3D printing process called Direct Metal Laser Sintering, or DMLS, to build “complex labyrinths” into their SLX and SLH suppressors designed for fume reduction. Previously, suppressors were made with machined baffles that were welded together, one by one.

“There would have been no way to get a tool in here to cut any of these paths or direct any of that gas,” Shoemaker said of the new suppressors. “It was game-changing for the entire suppressor industry because it unlocked all of these abilities to … make these complex geometries.”In service of developing reduced-toxicity suppressors for the Army and later the Navy, Sig acquired two specialized testing environments: the Crane box, invented at Naval Surface Warfare Center-Crane Division, Ind., to precisely measure released carbon dioxide as weapons fire in a confined space; and the Military Operations in Urban Terrain (MOUT) chamber, which now measures precise particulate amounts and concentrations of four gases: carbon monoxide, carbon dioxide, ammonia and hydrogen cyanide. Sig is the only non-military entity to possess the chambers.

While Shoemaker said the company is still seeking to make incremental improvements to the blowback reduction capabilities of existing suppressors — from, say, the current 70% reduction maximum to 75% — he also said the DMLS technology would make it easy to deliver a variety of suppressors specialized to maximize reduction of either sound, flash or fumes based on use case.

The Army has yet to ask for a mix of training suppressors and combat suppressors. But Shoemaker indicated it may emerge as a solution for a service that wants to have it all in terms of sound, flash and toxic gas reduction, and can’t practically have it all in one can. If so, the company will be ready.

“With DMLS, [engineers] can make a new design, and we can have it and shoot it three days later,” he said.