The Steyr M series of pistols employs the mechanically locked Browning short recoil method of operation with a linkless, vertically dropping barrel. The barrel is locked to the slide by means of a single rectangular lug around the barrel chamber that recesses into the ejection port in the slide. When fired, the recoil impulse from the ignited cartridge drives the barrel and slide back, locked together until the bullet leaves the barrel and pressures drop to a safe level. A locking block integrated into the frame then engages a lug at the base of the chamber and drives the barrel downward, separating it from the slide and terminating any further rearward movement while the slide continues back in a straight line.
The Steyr M series uses a very high grip profile which holds the barrel axis close to the shooter's hand and makes the Steyr M more comfortable to shoot by reducing muzzle rise and allowing for faster aim recovery in rapid shooting sequence.
Hammerless and striker-fired, the Steyr M features a double action only (DAO) pre-set trigger mechanism marketed as a "Reset Action" trigger. When the trigger is in the forward position, the firing pin spring remains lightly compressed (pre-cocked by the forward motion of the slide as it returns to battery). Pulling the trigger all the way to the back will compress the firing pin spring completely, draw the firing pin fully to the rear and position the trigger bar to release the firing pin and fire a round. The trigger travel is 4 mm (0.16 in) with a pull weight of 25 N (5.6 lbf).
The pistol has a multi-stage safety system consisting of two automatic internal safeties, two external trigger safeties and a manual lock safety. The first external trigger safety acts as the primary fail-safe. A small, spring-loaded inner trigger is housed in a wide, outer trigger and cannot be actuated unless the inset trigger is depressed first. This keeps the trigger from being pulled by an inadvertent off-angle trigger pull. This trigger safety also activates and when released—deactivates the two internal safeties: the firing pin and drop safety. The firing pin safety is contained in the pistol’s slide and blocks the longitudinal movement of the striker. The second trigger safety is an optional, manually operated plastic bar located inside the trigger guard and projecting out from the base of the pistol’s frame when activated, revealing a small white dot. This indicates that the pistol is currently incapable of being fired. It is used as an additional safety that disables the trigger with the firing pin spring cocked (after reloading the pistol). This safety is engaged by simultaneously pushing in two buttons on both sides of the frame and then deactivated by simply lifting the trigger finger and pushing the bar up and into the pistol's frame, thus allowing the trigger to be pulled back and the weapon fired. These safeties enable safe handling of the pistol with a round present in the chamber (the so-called "cocked and locked" condition) and allow for rapid deployment and immediate firing; this arrangement however does not permit the firing mechanism to be re-cocked in case of a misfire after the trigger has been pulled.
Other safety features include a loaded chamber indicator and an integrated limited access lock operated using a key to prevent unauthorized use. The latter key can be either a handcuff key or a special factory-supplied key. If required, the access lock can be omitted. The locking mechanism is located above the trigger area of the pistol and is characterized by a small circular plate with two holes in it (in the police version of the pistols there is a handcuff key hole instead of the two small holes). It has two positions: "F" and "S". When pushed in and rotated to the "S" position with the provided key, the lock disables the trigger and barrel and prevents the pistol from being disassembled. This unique system of limiting access to the weapon was patented (U.S. Patent 6,212,812) by Friedrich Aigner in 1999.
The pistols are fed using a detachable steel magazine of the single position feed type with the cartridges arranged in a staggered column pattern. The magazine’s follower and floor plate are fabricated from polymer. The magazine catch-release is located on the left side of the frame, directly behind the trigger guard. After expending the last cartridge from the magazine, the pistol’s slide remains locked open on the metal slide stop, located on the left side of the frame and operated with the thumb.
The Steyr M is equipped with fixed, low-profile iron sights. The unique sighting arrangement consists of a triangular front sight and a trapezoid rear notch that lead the eye to the target for quicker target acquisition and allow for instinctive aiming. The front sight contains a non-luminescent white triangle contrast element designed to mate with two white rectangles on the rear sight. Optional tritium-illuminated low light situation sights can also be fitted to the Steyr M; these have a conventional rectangular profile. The pistol’s frame also has proprietary mounting rails for attaching accessories, such as a tactical light or laser pointer.
The pistol’s design takes advantage of modern manufacturing techniques: the slide is precision-milled from steel; the frame is an injection-molded synthetic polymer and parts of the trigger and striker mechanisms are pressed from sheet metal. For the purpose of regular maintenance, the pistol is stripped down into the following components: the barrel, slide, recoil spring, frame and magazine.
While the Steyr M is frequently compared to Glock-series pistols (both are polymer-framed striker-fired pistols, with Tenifer finishes), there are several differences in the details of the design. For example, the M-series had a fully supported chamber in all chamberings from the start (Some Glock models also had this feature from the start, other Glock models evolved to having more supported chambers when compared to their original internal layout), unique triangular/trapezoid sights, a loaded chamber indicator below the rear sights (on third and later generation Glock pistols this feature is present on the extractor on the right slide side) and a different grip angle (111°).