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If you’re interested in purchasing a new-production SIG Sauer semi-automatic pistol, it’s worth understanding the difference between the civilian P320 and the military-issue M17. This way, you can more accurately determine whether one weapon is sufficient for your needs.
M17 Modular Handgun System (MHS)
The United States Army adopted the Beretta 92F as the M9 in 1985. The M9 is a double-action/single-action (DA/SA) aluminum-framed semi-automatic pistol fed from a 15-round detachable box magazine.
This represented a significant increase in magazine capacity compared with the 7-round magazine of its predecessor — the venerable M1911A1. The M9 was also the first 9mm semi-automatic pistol that the United States Army adopted as its official sidearm.
However, due to many complaints from military personnel in surveys, the U.S. military began searching for a suitable replacement.
In 2011, the United States Army and Air Force held the XM17 Modular Handgun System (MHS) competition. Eight manufacturers, including Beretta, CZ, and Glock, submitted sample pistols.
However, in 2017, SIG Sauer announced at the SHOT (Shooting, Hunting, Outdoor Trade) Show that the U.S. Army awarded the company a contract for its P320 MHS. This pistol was designated the M17 and M18.
M17 and M18 Pistols
Both the M17 and M18 are semi-automatic, striker-fired, recoil-operated modular pistol designs. The M17 is the full-size service pistol with a 4.7” barrel, whereas the M18 is the subcompact variant with a 3.9” barrel.
While the M17/M18 is chambered in 9×19mm Parabellum, the MHS can be chambered in .357 SIG and .40 S&W for increased stopping power. However, what are the differences between the commercial P320 and the M17/M18?
You may notice the addition of an ambidextrous manual thumb safety on the M17. While manual safeties are more common on hammer-fired semi-automatic pistols, some manufacturers still include them in striker-fired designs. SIG and Smith & Wesson are two notable examples.
The military mandated the M17’s manual safety. This is a natural extension of its previous handguns having a manual safety (M1911A1), safety/decocking lever (M9), or strictly a decocking lever (SIG P226).
This feature can add peace of mind but requires additional training. You should be able to disengage the manual safety when you draw the pistol and re-engage it as you reholster the weapon. Some gun owners regard this feature as superfluous, but those who grew up with 1911-pattern handguns appreciate the extra layer of safety.
Both the civilian P320 and the M17 feature a Picatinny MIL-STD-1913 rail on the dust cover for mounting accessories. A common complaint regarding the M9 pistol was that there was no convenient way to attach a light or laser.
However, unlike the P320, the M17 features an optic cut. This enables you to attach a miniature red-dot (MRD) sight — an increasingly popular type of sight for competitive target shooting and law-enforcement/military service.
In this system, SIG mills a slot in the slide's top and inserts a cover plate. The cover plate hides tapped holes to which you can screw an adapter plate and sight. This optic cut is compatible with the ROMEO1 PRO.
MRD sights allow you to achieve a higher degree of accuracy than iron sights and provide increased visibility under low-light conditions.
The P320 features three-dot fixed combat sights — standard for many duty pistols. In contrast, the M17 is equipped with night sights for increased visibility under low-light conditions.
SIG offers several grip modules for the M17 to accommodate different hand sizes. At the same time, these grip modules must be interchangeable between the full-size and compact variants of the pistol. As a result, you’ll notice that the frame does not extend to the front of the slide in the M17 the way that it does in the P320.
The stock P320 is an all-black pistol, but the M17 and M18 feature a coyote-tan color scheme — appropriate for Middle Eastern operations — on both the frame and PVD-coated stainless-steel slide. This reduces contrast and acts as a kind of camouflage. While this may not be necessary in a civilian context, colors like desert tan and flat dark earth continue to be popular among pistol shooters.
Loaded Chamber Indicator
No mechanical safety device is a substitute for the strict observance of firearms safety rules. Some gun owners find loaded-chamber indicators to be useful, but this is not a replacement for observing Rule 1 — “All guns are always loaded.” You should still make a habit of checking the chamber of a gun manually when you handle it.
That being said, both the SIG Sauer P320 and M17 handguns feature loaded-chamber indicators for visual and tactile confirmation of the weapon’s loaded status. In the P320, this is strictly a visual indicator. A port in the barrel's rear allows you to see the cartridge brass of the chambered round. In the M17, the indicator takes the form of a steel block that the cartridge raises.
The M17/M18 is fed from a 17-round magazine as standard; however, optional 21-round magazines are also available for increased firepower. These high-capacity magazines extend from the pistol frame.
Regardless of whether you possess a commercial P320 or a military-issue M17, the magazines are fully interchangeable, including between the full-size and compact variants. While the P320 ships with one 17-round magazine, it will accept both the military-specification 17- and 21-round magazines and vice versa.
Some differences between the M17 and the P320 are subtle. But part of being a responsible consumer is being informed. The civilian variant is an outstanding handgun, but the M17 has a few extra features.
However, many of these differences are not critical to functionality. If you want a high-quality semi-automatic pistol for self-defense or competitive target shooting, either pistol can serve you exceptionally well.
Civilian P320 or Army M17, SIG Sauer manufactures several high-quality striker-fired semi-automatic pistols. Most of the differences between the two are minor, but if you want a manual safety, optic cut, coyote-tan finish, or tactile loaded chamber indicator, consider the M17.