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LWRCI’s New Short Recoil/Delayed Blowback SMG-45 Is a Fresh Take On the Subgun

The touchstone of the submachine gun world has been, and likely always will be, Heckler and Koch MP5’s roller-delayed blowback system. But, most subguns that’ve come to market since seek to differentiate themselves with a simpler operating system that’s less expensive to manufacture and less expensive to maintain.

LWRC International takes a nearly hold-my-beer approach with its complex-looking, yet elegant-acting short recoil/delayed blowback operating system. From the outside, it looks like it could be a stout little AR, but under the skin it’s a whole new roadhouse.

Early 2019 brought the introduction of the SMG-45, a 45 ACP-chambered submachine gun. While new for 2019, this project began at least four years prior at the request of a foreign military customer. This customer went to LWRCI looking for a subgun upgrade for its 9mm-armed soldiers with security and personal protection responsibilities.

The Aimpoint PRO is an out of the box RDS ready for any carbine or submachine gun.

As government acquisitions sometimes go, the project withered and the prototypes were shelved, but not before it was shown to attendees at the 2015 SHOT show. Fast-forward several years and the U.S. firearms market is infatuated with pistol-caliber carbines (PCCs) and subguns again. By consumer demand, the project was put back into motion at LWRCI for a commercial release.

Operating System

The SMG-45 uses an inertia-driven, delayed blow-back design. Instead of a roller-delayed system found in Heckler & Koch’s genre-defining MP5 subgun or the direct blow-back design found in many other submachine guns, the SMG-45 uses what LWRCI describes as a short-recoil action that includes a moving barrel.

During firing and the initial steps in the cycle of operation, the barrel and bolt are linked by a locking collar. This creates a larger mass to better absorb recoil and slow the bolt when it begins to move. As the bolt and barrel travel rearward under recoil, the locking collar engages the top of the feed ramp and is pulled downward, decoupling the bolt from the barrel. At this point, the barrel stops after moving about a 1/4 inch, but the bolt continues rear-ward, extracting the spent case and performing the remaining steps in the cycle of operation.

Linking the bolt and barrel together during the initial portion of travel slows the bolt and allows time for the chamber pressure to peak and start to drop. With the chamber pressure spike all but dissipated by the combined mass of the barrel and bolt before things really get moving, the SMG-45’s decoupled bolt alone is a lot lighter than the bolt of a straight blowback action. The lower mass results in lowered felt recoil and reduced sight movement during operation compared to contemporary .45-caliber subguns.

While it shares some features of an AR-15, read the owner’s manual before taking the SMG apart.

Many of the PCCs available today, particularly AR-15 based versions, use pistol magazines. LWRCI engineers recognize the economic and operational efficiency of a subgun that shares the same mag as a pistol, but to an engineer it’s not the optimum solution for a carbine. Pistol magazines have a steep feed angle and a very forward raked body tube, because they’re designed to fit within a pistol’s grip. Additionally, there aren’t a lot of extended (18-20+) pistol magazines known for reliability. These attributes can be awkward and unreliable when adapting a pistol magazine to a rifle platform.

During the design phase of the SMG, LWRCI engineers selected HK’s UMP 45 ACP magazine to shortcut the development process for the original government customer. Even though the LWRCI SMG-45 uses the UMP magazine, it’s an entirely new platform with no other HK commonality or compatibility.


There’s obvious evidence of the AR’s design influence on the SMG, and not just milling out the lower receiver to take a pistol magazine. Handling the SMG for the first time feels very familiar thanks to the AR-15-like control layout. In line with other LWRCI guns, the machining is free of tool marks, lines are even and straight, and the anodizing is free of imperfections. The receivers and push pins are tight but fit without binding, and nothing rattles on the gun.

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