Sig Sauer P320 vs. M17 vs. M18: What’s the Difference?

I distinctly remember being at SHOT Show 2017 when the big news came in that Sig Sauer had won the Army’s Modular Handgun Contest.

This contest had seemingly gone on forever and cost an obscene amount of money. Sig was declared the winner with their M17 and M18 series of pistols.

Like every other hack gun writer, I rushed to publish a story with a comment from Sig Sauer.

Since then, the Marine Corps, Navy, and Air Force have all adopted the M17 and M18 series pistols. Sig has even produced both standard and commemorative versions for the gun-buying public.

The P320 existed well before its military adoption, but they did have to make a few changes to the platform to meet the testing requirements.

You might be wondering what makes the P320 different from the M17 and M18.

Well, I’ve got great news for you — that’s exactly what we are discussing today…So keep reading if you want to learn more about these three pistols.

What is the Sig Sauer P320?

It’s a handgun, obviously, but it has some nontraditional design elements.

Sig utilizes an internal chassis system that is the serialized portion of the firearm. It can move from frame to frame, slide to slide, and even caliber to caliber easily. This is also present in the M17 and M18 models.

The P320 series of firearms are semi-automatic handguns utilizing a polymer frame with a double-stack magazine.

They are striker fired and available in various major centerfire handgun calibers, including 9mm, .40 S&W, .45 ACP, 10mm, and even .357 SIG.

Using a more modern design, the P320 broke away from Sig’s successful tradition of mostly metal-framed DA/SA guns.

Since its introduction, they’ve been adopted by dozens of police agencies and several military forces, including Australia, Costa Rica, Ukraine, and Canada.

What About the M17 & M18?

Every M17 and M18 is a P320…but not every P320 is an M17 or M18 pistol.

The P320 series is a family of pistols that encapsulates different sizes and designs, like the XCarry, the AXG, and of course, military variants.

While still a P320, the M17 and M18 are just specific sub-models built to meet the standards required by the U.S. Army.

P320 vs. M17 vs. M18: What’s the Difference?

At their core, they are the same gun, but subtle differences distinguish them.

Each of these features has made it to other P320 variants, but the sum of these features is what makes a gun an M17 or M18.

One of the most significant differences is that all M17 and M18 series feature an optics cut. While plenty of P320s are cut for optics, every M17 and M18 is cut for the Leupold Delta Point Pro footprint.

The M17 and M18 series also feature an ambidextrous safety selector. The US military really loves safeties on their handguns. Additionally, the slide stop/lock is low profile and ambidextrous as well.

These guns are also fitted with a loaded chamber indicator in front of the optic’s plate and above the barrel.

This was the first P320 to feature a loaded chamber indicator, but it’s becoming more common on the platform.

Its tan color was another requirement by the U.S. Army. One of the least noticeable changes was the use of spanner screws instead of normal screws. The Army wanted spanner screws to reduce the risk of unauthorized disassembly procedures.

However, if you purchase a commercial M18 or M17, it uses traditional screws and not spanner screws.

The M17 and M18 share a frame. On the M17, the frame doesn’t extend to the end of the slide. On a standard full-sized P320, the frame goes all the way to the end of the slide and sits flush.

How the M17 & M18 Differ From Each Other

Size is the main difference between the M17 and M18 series.

Both guns feature the same-sized frame, which is a full-sized grip with a compact-length dust cover. This allows both guns to use the available 17 or 21-round magazines.

With the M17, soldiers get a full-sized handgun with a 4.7-inch barrel. The obvious benefits are a longer sight radius, a slight velocity increase, and an easier-to-control gun.

Check out our full review of the civilian Sig M17!

On the flip side, the M18 uses a compact-length slide with a 3.9-inch barrel, making the weapon lighter and handier overall. The compact slide with a full-sized frame is akin to a P320 Carry model.

Overall, the M18 seems to be the more popular choice, both in the military and civilian worlds. The Air Force, Navy, and Marine Corps specifically chose the M18 series for adoption.

The Marine Corps is not only replacing the M9 but also its M1911s used for Force Recon and the Glock M007 pistols used by certain military police units.

Other M17 & M18 Models

Sig isn’t one to just produce a single pistol and be done with it. There are two interesting variants worth mentioning.

Tomb of the Unknown Soldier M17

The Tomb of the Unknown Soldier is a memorial at Arlington National Cemetery dedicated to U.S. service members whose remains haven’t been identified. It’s famously guarded by men of the 3rd Infantry Battalion of the U.S. Army.

These ceremonial soldiers are now armed with very special models of the M17. These pistols are metal-framed, all-black M17s. Only four exist, and they are named Silence, Respect, Dignity, and Perseverance.

The names of these pistols are inscribed on their slide. At the rear, the cocking serrations are replaced with XXI to reference the 21 steps the soldiers take in their duties and the 21-gun salute.

Silence and Respect and daylight duty pistols with brown wood grips.

Dignity and Perseverance are night-duty pistols with black wood grips. The wood was taken from the deck of the USS Olympia, the first ship which carried the first Unknown Soldier to the United States.

The front Sight lacks a tritium vial and instead uses a glass vial containing dust from the tomb’s restoration. Across the red dot plate sits an engraving that reads Peace, Victory, and Valor.

These are beautiful pistols and are really M17s in name only.

General Officer’s M18

Ever since World War II, the military has had a tradition of issuing Generals a special handgun that they can purchase when they retire.

In the past, it’s been the Colt Pocket Hammerless, the M15 1911 pistol, and the M9 GO.

These days the General Officer Pistol is the M18. It’s fairly standard and is only differentiated by the serial number. General Officers get a GO prefix, and then they can choose their own serial number.

Some generals use that space to commemorate their position or a unit special to them. Other than the serial number, they are your basic M18 pistol.

Final Thoughts

It’s unclear how long the M17 and M18 series will serve. It seems unlikely they will fade away anytime soon, as they have only recently been adopted.

Past experience has shown that modern handguns can last decades.

The modular nature of these guns will likely help them maintain a long lifespan. Until we have a significant change in ballistics, propellants, or projectiles, it’s unlikely we’ll change handguns anytime soon.

What do you think of the M17, M18, or P320? Let us know in the comments below! Still trying to figure out all of the other P320 models? We got you covered with our article, Sig Sauer P320 Models: Meet the Lineup [Ultimate Guide].

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