The B&T USA USW-320 Universal Service Weapon upgrade chassis will fit the SIG Sauer P320 or the military’s M17. mfg photo


You may remember rumblings about something called the Universal Service Weapon back in the summer of 2016. It’s now a reality.

B&T USA has launched a new enhancement for the SIG Sauer P320, and the U.S. Army’s M17 service pistol, based on the P320: the Universal Service Weapon Upgrade Chassis. Technically, it’s an enhanced polymer lower, to use AR terms, for the P320 modular platform.

Dubbed the USW-320 for short, the chassis weights in at 6.63 ounces and is fully ambidextrous with installation taking just a few minutes.

The idea of the Universal Service Weapon is that it would be a duty firearm, capable of being carried in a conventional handgun holster, that could also stand in for a pistol-caliber carbine when needed for police and military by including an optic and a minimalistic folding buttstock.

According to this story from, users just have to remove the serialized trigger group from the P320 and drop it into the new chassis, which is an entirely new frame. Then the P320 (or M17) slide and magazine are assembles as normal—just as the modular handgun was designed to do.

The idea of the USW is that it can be carried and used like a conventional handgun, but can act as a pistol-caliber carbine with a shoulder stock if needed by law enforcement and the military. mfg photo


The story says that the chassis doesn’t come with any special restrictions, since the firearm’s serial number is located on the trigger group only. That means the USW-320 itself isn’t considered a serialized firearm.

However, once the whole thing is put together, you still have a handgun with a folding buttstock, which would be considered an NFA firearm requiring a tax stamp when it comes to civilians—but that won’t be a concern for LEOs and the military. It’s not known if the product will be made available for civilian purchase in any way.

The new B&T polymer lower on its own. mfg photo


“SIG’s P320 striker-fired pistol is unique in that it gives the user complete modularity by allowing him or her to change frame size, fit and even caliber by simply swapping out the serialized trigger group,” Jon Scott, VP of Sales at B&T USA, said in press release. “The USW-320 builds on this modularity by providing a chassis that adds the stability of a folding stock along with ambi controls and an integrated Picatinny/NAR accessory rail.”

The story says the USW-320 will be available in April, though no price has been released.

The product photos released back in 2016 included a bracket mounted on the rear of the chassis that could accommodate an Aimpoint Nano optic. The placement had some wondering if the only way to operate the slide would be to grasp it by the front serrations hear the muzzle. However, the photos of the chassis coming to gun shops shows a SIG red dot mounted to the slide of the actual handgun with raised iron sights.

A photo of an earlier version of the USW chassis released in 2016.
A photo of an earlier version of the USW chassis released in 2016. photo from