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The Difference Between the Sig Sauer P320, M17 & M18

How does the Sig Sauer P320 differ from the M17 and M18 military versions? We deep dive into these pistols to see what features are different.

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.

The M17 is a formidable weapon designed to operate in the military theater
Sig P320 M17

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.

U.S. soldiers firing the Sig M17 modular pistol.

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.

Table of Contents


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.

From its inception, the P320 was designed to be completely modular.

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.

Popular Pistol Calibers

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.

Sig Sauer AXG Profile
The P320 has evolved to include steel-framed models, such as the AXG Scorpion pictured above.

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

How Are the M17 & M18 Different than the Sig P320?

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.

Sig Sauer M17 (rear) and the Sig Sauer M18 (front). (Photo: Sig Sauer)

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.

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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.

Army Sig Sauer
A US soldier with the 101st Airborne Division fires the new M17, or Modular Handgun System, at the 5th Special Forces Group (Airborne) indoor range on November 28, 2017. (Photo: U.S. Army, Sgt. Samantha Stoffregen)

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.

The spanner screw, located on the frame above the trigger housing, is also referred to as an “anti-tampering device.” (Photo: Soldier Systems)

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.

Sig M17 (Photo: U.S Army, Sgt. Samantha Stoffregen)

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!

New Military Standard
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Prices accurate at time of writing

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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.

A U.S. Marine holding the newly adopted Sig M18 (Photo: US Marine Corps)

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.

at Kygunco

Prices accurate at time of writing

Prices accurate at time of writing

Available Coupons

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.

The black chrome style finish is unique to these models. (Photo: Sig Sauer)

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.

Each gun has the name relief engraved on the bottom of the dust cover. (Photo: America’s 1st Freedom)

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.

Guarding the Tomb of the Unknown Soldier is a very symbolic and elegant process, and these pistols are built to match that. (Photo: Soldier Systems)

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.

A Sig P320 GO is present during a ceremony held to honor the promotion of Texas Army National Guard Colonel Amy F. Cook to the rank of Brigadier General on July 11, 2020. (Photo: U.S. Army, Charles E. Spirtos)

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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5 Leave a Reply

  • Commenter Avatar
    Frank Hardush

    This was a really well written article on the P320 vs M17 vs M18, it revealed a lot of information about the firearm I had no knowledge of. I really enjoyed reading the information on the Honor Guard versions. If you have never visited the "Tomb of the Unknown Soldier" or witnessed the Changing of the Guard, it should be on your must do list or bucket list. It is a true portrayal of honor and respect. I had the chance to witness this ceremonial Changing of the Guard while stationed just outside DC as a young soldier. It has stuck with me ever since(1992). (sorry off track) Back to your article it was a really good and informative read. Thank you

    March 5, 2023 7:20 am
  • Commenter Avatar

    If given a choice I would choose a new m9 or a Sig 226 MK 25 ...The reason troops did not like the M9 is because the were about wore out and poorly maintained...The 1911 is my fave, but not a bare bones mil spec model or armory guns....Those new guns will suffer from the same problem left in the hands of military armories...They think guns last forever with the same parts...Troops ought to be able to purchase their own personal handguns like in some past wars (and SPEC OPS)...If it was left up to me, IT WOULDN"T BE THAT MONSTROSITY!...

    March 1, 2023 10:16 am
  • Commenter Avatar

    This was a very good article. I really appreciated reading about the four special M17s carried by the soldiers that guard the tomb of the unknown soldier at Arlington. Thank you.

    March 1, 2023 8:49 am
  • Commenter Avatar
    Christopher Saari-Poulter

    Off topic but I gotta know, is there any plans to test out the new Palmetto State Armory Sabre line?

    March 1, 2023 2:37 am
  • Commenter Avatar

    I have heard, only hearsay, that the military version of the P320 has different internal safeties than the civilian version. I understand that there are external, manual safeties on the M-pistols. But are there differences on the internal safeties between the P320 models, military and civilian, to avoid an unplanned discharge? Btw, great article!

    February 28, 2023 8:24 pm
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