Sig Sauer P320 M17 vs. M18: What Are The Differences?

Sig Sauer M17 vs. M18, what is the difference between the two pistols that pushed the Beretta M9 out of service?

Sig Sauer won the MHS trials in January of 2017 against Glock, FN, Beretta, CZ, and the list goes on.

Many would argue that Glock should have won the MHS trials, but the Army wanted modularity in their new pistols.

And the Sig Sauer entries had more modularity than any other firearm on the list.

I mean, how much modularity can you ask for when you can literally change the whole firearm by removing the takedown lever?

The differences are few, but we’re going to be talking about what these differences are and why they matter.

Sig Sauer M17 – The Big Brother

The Sig Sauer M17 is a full-sized, striker-fired, semi-automatic pistol that Sig Sauer brought forward in 2011 when the U.S. Army requested a replacement for the Beretta M9.

Its highly modular design allows virtually any part to be replaced, including the grip module, by removing the takedown pin and the fire control unit.

It’s optics-ready and uses the Leupold Deltapoint Pro footprint. Of course, Sig Sauer makes their own pistol red-dots that use the same footprint.

It’s fielded by the U.S. Army with some smaller uses in the Navy, Air Force, and my beloved Marine Corps.

Sig Sauer M18 – The Little Brother

The Sig Sauer M18 is a carry-sized, striker-fired, semi-automatic pistol that Sig Sauer entered alongside the M17 since the MHS contract called for both full and carry-sized pistol variants.

It shares almost everything with the P320 Compact. It even fits the same holsters.

It has the same modularity as the M17 but sports a shorter barrel and slide than it’s full-sized older brother.

The M18 is also optics-ready and uses the Leupold Deltapoint Pro footprint that Sig Sauer uses on their pistol red dots.

The Sig Sauer M18 is fielded by the Air Force, Navy, and Marine Corps with smaller uses in the Army.

Both pistols come out of the box with (1) 17-round magazine and (2) 21-round magazines. 

With all these similarities, you may ask yourself, “Well, what are the differences between the M17 and the M18?”

And the answer is simply the length of the slide and barrel.

The M18 sports a 3.9-inch barrel, whereas the M17 is standard with a 4.7-inch barrel. The differences are very few, but when you chop an inch off the barrel, the performance in ballistics is where you start to see the real difference.

And, of course, a small bit of weight.

The M17, being the longer pistol, has a bigger sight radius, less felt recoil, and increased bullet velocity over the M18.

But first, let’s talk about…

Accuracy

Anyone who has spent time shooting smaller and larger pistols knows how snappy smaller pistols can be in comparison to their larger cousins.

This is due to the extra weight that sits on the front of the larger firearm, which results in less muzzle flip.

Why do you think competition guns are longer than the old lady’s leg hair in the winter time?

And smaller pistols, being that there is a minimal weight holding the front end down, typically have more muzzle flip. This makes follow-up shots a bit harder, resulting in less accurate shots.

So, by default, the M18 is harder to get back on target than the M17 since the barrel length on the M17 is longer than the M18.

And if you’re going for accuracy, then the M17 is where you should be looking. Those who want to carry their Sig may want to look into the M18 (don’t worry, accuracy is still good).

Weight

I know, this much is obvious. So without being too redundant, the weight of the M17 is about half an ounce heavier than the M18.

As I said above, this helps with accuracy and control over the pistol. So this be useful for those of you who are looking for a sidearm in their boogey loadout or to LARP around the woods with.

Now I’m not saying the M18 is not a good option. Hell, the Marine Corps love it for its handiness. I own an M18 myself (gotta keep the tradition alive), and I have owned the M17 in the past. Ultimately, I went with the M18.

I’m just a sucker for flush slides and grip modules.

Bullet Velocity

Basically, how quickly can the round get to the target?

Since the M17 has a longer barrel, you can bet that the bullet velocity on the M17 is quicker than the M18.

Not that you’d notice. From the naked eye, and when the round hits the target, neither you or the target will be wondering how fast that round got there.

But the big difference lies in the penetration.

Now I don’t have any ballistics gel or anything fancy, but any shooter who has watched their fair share of ballistics gel videos knows that longer barrels tend to fare better with bullet penetration.

So if penetration is what you’re after, the longer, the better. It’s a good thing I don’t have to say this in front of a crowd because keeping a straight face while doing so is hard.

But you get the point.

Carry-ability

Depending on your planned usage for the Sig M17 or M18, the pistols’ sizes are a huge factor.

For just a moment, and since everyone knows these firearms well, let’s compare the M17 and M18 to the Glock 17 and 19.

The Glock 17 is a full-sized pistol that most individuals may not want to carry since it’s larger and harder to conceal. There are some individuals who carry the Glock 17, but they usually have larger frames and can keep the behemoth hidden.

That would be the M17.

On the other hand, you have the Glock 19, which is the most popular handgun in the United States. It’s compact enough to carry but still leaves enough room for you to get a good grip and take care of business. Should the need arise.

That would be the M18.

Now I’m not saying that one can’t carry the M17 or the Glock 17, but for concealed purposes, most individuals will fare better with the M18 or the Glock 19.

But that’s for concealed carry; duty or boogaloo loadout pistols are a bit different.

Say you’re going full kit. Plate carrier, drop-leg Safariland holster, and the rest of the works, you don’t have to worry about concealing now, do ya?

Exactly.

And in those terms, when you’re out in the woods dragging your boots through the dirt, having a longer pistol might be a great idea since you get a bit more accuracy and bullet velocity out of the M17 over the M18.

But, to each their own. Carry a damn Desert Eagle if you wish.

Although the differences between the M17 and M18 are slim, there are some important things to consider if you are here to find out which Sig Sauer pistol you plan on sealing the deal with.

If you plan on carrying…

Then the M18 will suit you better. The smaller slide and barrel easily tuck away into your chosen concealed carry holster and make a great alternative to any Glock pistol on the market.

There are more options for concealed carry holsters for Glocks, though.

I speak on this from experience. My everyday carry pistol is a Sig Sauer M18 that I pretty much changed everything on.

I featured it in my 3000-round review of the M18, and I have to say that even though I have a Surefire X300U on it along with a Holosun 507c, it’s still pretty easy to carry in the summertime.

It’s even easier to conceal carry if you throw a Streamlight TLR-7 on there and a low-profile optic like a Trijicon RMR (see our RMR Type 2 review).

And if you really want to go as small as possible but still want real estate to give your pinky a place to rest, try the P365 X-Macro.

Duty Use

Now for those of you who plan on carrying the M17 out in the open, whether it be for law enforcement purposes or good ol’ LARPing around in the woods, then the M17 is better suited for these scenarios.

The longer barrel gives you better accuracy, and since you won’t have to worry about the barrel jabbing you where the sun doesn’t shine, it won’t constantly remind you that you have a firearm pointed at your no-no square.

Trust me, I’ve been there. It’s the reason why I got rid of my M17.

But when I was open carrying, LARPing through the woods, and having a good time, nothing beat my M17.

The M18 still does a great job in that area. So no worries there.

Modularity

The beautiful part of the Sig Sauer M17 and M18 is the modularity of both firearms. Neither is more modular than the other, and you can change the whole firearm around by simply removing the takedown pin.

That’s how I was able to put a Wilson Combat grip module on my M18.

Since Sig Sauer uses an internal chassis system that doubles as the serialized portion of the firearm, changing the whole configuration is as easy as pissing off the old lady when you come home with a new firearm.

Again, I speak from experience.

So, if you decide that you want to change your M17 or M18 into, say, an X-Carry Legion, all you have to do is order the parts from Sig Sauer. No background checks are needed.

This is the reason why the M17 and M18 won the MHS trials. And why Glock lost. Modularity.

Speaking of which, I’m going to need those Spectre Comp Blackout parts soon.

FN 509 Tactical

I must admit, if I could go back in time and pick another pistol, I would have gone with the FN 509.

I also must admit that I went with the M18 due to the large magazine capacity. And then I realized that the 509 actually has a 24-round magazine that looks amazing when it’s sitting inside of the firearm.

Albeit pricier than the Sig M17 and M18, you do get what you pay for. The 509 Tactical comes with suppressor height sights and a threaded barrel. Two things that I wish my M18 came with from the factory.

Sure, it’s not nearly as modular as the M18, which is another reason why I went with it. But there are many aftermarket options that would have set my soul straight.

Walther PDP Pro SD

The PDP Pro SD is another pistol I sometimes kick myself in the butt for not thinking of when I was looking for a new pistol.

Much like the 509 Tactical, the PDP Pro SD also comes with a threaded barrel. But the PDP Pro SD has a flared magazine well and a trigger that is to die for.

The Walther PDP also won Pistol of the Year from ICA and Guns and Ammo magazine. Once you get your hands on it, you can easily see why.

Sooner or later.

Even though the differences are very few between the Sig Sauer M17 and M18, they both strive in their own areas and will benefit the shooter in different ways.

The M17 strives in duty use. The M18 does best in concealed carry scenarios.

Now, the beauty about this is that if you buy either, you can easily get the other by just ordering the slide, barrel, and recoil spring from Sig Sauer. And you can change your M17 to an M18 and vice versa in a matter of seconds.

So don’t worry about which one you should buy. You have two in one. It is the most modular pistol on the market, after all.

See you on the range, fine shooter.