The Sig Sauer P320.
The Sig Sauer P320. author photo

When I look at a new gun, I like to spot the one big thing that’s different. I always hope there is something noteworthy and unique, or else it would be like plenty of other guns, and that would be a boring review, wouldn’t it? With the Sig Sauer P320, finding that one big area of differentiation was easy: its modularity. Well, technically speaking, I suppose there are three big areas because that modularity concept applies to fit, size, and caliber.

Modular Fit

Most modern handguns come with optional grip back strap pieces of different size. The idea is that, with one of these inserts, you make the grip larger because adding a larger back panel makes the back bigger. But that’s exactly what the back strap approach does – make the back strap bigger. It’s not a holistic approach to grip size. If you want to fit a P320 to a shooter with smaller or larger hands, you replace the whole lower frame. Sig offers small, medium and large grip size frames to fit a wide variety of hand sizes. That sounds complicated and expensive, but it’s not, as we’ll see in a minute.

Sig Sauer P320
The “gun” part of the P320 is actually the steel trigger assembly. All of the other components are just parts. author photo

Modular Size

If you use a gun, it can be awfully handy to have different sizes for different purposes. If you choose to carry one concealed, something more compact is a plus, because it’s easier to hide and lighter to lug around. If it’s for home defense, something physically bigger can be a benefit as a larger and longer gun is easier to aim and control and it holds more cartridges. If you like to compete in shooting sports, a larger gun with more capacity is also desirable.

What would be really cool is having the same exact gun fit all these needs. If it had the same trigger and feel of operation, the same mode of operation and the same overall feel, you’d be a better all-around shooter because you’re always using the same basic gun. That’s exactly what Sig did with the P320 platform. Besides the frame, the ability to swap out the barrel and slide is also part of the deal. The best part is that you can do all that without more background checks and paperwork with your dealer. You can even order the components online. Sig P320 components will be available to configure full-size, compact, and subcompact sizes. Hold this thought too – we’ll explain in a bit.

Sig Sauer P320
You can order a kit like this to change size and/or caliber. mfg photo

Modular Caliber

If you’re going to figure out how to make the same gun fit different shooters and come in completely different sizes, why not allow the owner to change calibers too? Certainly military and law enforcement users may have a desire to use different calibers for different purposes, but us regular folks might want to do that too. What if you could, using the same serialized gun, shoot lower-cost 9mm loads to practice or compete on weekends, but change to something bigger like .357 Sig, .40 S&W, or even .45 ACP when you want to use the gun for defensive purposes? Well, the P320 will let you do that too. Next, we’ll explain how.

Sig Sauer P320
This Sig Sauer P320 came with two magazines and a Kydex holster, all packed in a hard plastic carry case. author photo

A Different Approach to Modularity

Most handguns are legally defined by the frame itself, which contains the trigger, hammer, striker, or whatever other components make the gun go bang. Since the part with the serial number comprises most of the gun, it’s not really feasible to swap major components.

The P320 takes an entirely different approach. Sig designed the pistol so that the “legal gun” is just a single modular system that contains the trigger and striker system. You drop that into the frame of your choice, and stick the barrel and slide of your choice on top. The modular “gun” assembly doesn’t know or care what caliber you’re shooting, so that’s how you can even change your “gun” to a completely different caliber.

It’s a great idea, especially since the most important parts to keep identical across various gun configurations are the trigger, striker, and operating controls. If you buy a Sig P320 and accessory parts to turn it into different handgun configurations, you won’t be shooting similar guns or guns that feel like your other ones. You’ll actually be shooting the exact same gun.

Sig Sauer P320
Note the cutouts on the bottom of the magazine well. These allow you to grip a stuck magazine for quick removal. author photo

Other Features

First of all, the Sig Sauer P320 is a striker-fired, semi-automatic pistol. Without getting into the weeds, a striker-fired pistol is designed to offer the same exact trigger pull for every shot, first to last. Inside, the striker (the firing pin, more or less) is always partially tensioned. The trigger press cocks it the rest of the way, then releases it. It’s this partially cocked process that allows the trigger press to be moderate in weight. On the pistol I tested, the trigger broke at 6 ½ pounds. Subjectively speaking, I would say that it feels lighter than that, probably owing to the smoothness of operation and the large, smooth trigger face.

Sig Sauer P320
This P320 came with steel Sig Night Sights. Tritium inserts keep the sights glowing in the dark for a decade or so. author photo

The P320 is also built to be friendly to right and left-handed shooters. The large magazine release button is easily reversible. Slide lock levers are present on both sides of the pistol, so there is no function lacking on the proper side for lefties.

The P320 features a Picatinny rail for attachment of lights and lasers. There are aggressive cocking serrations on the slide both front and back. The sights are steel, and while you can order standard three-dot sights, it seems that most P320s are coming equipped with Sig Tritium night sights.

Speaking of steel, even with the polymer frame, you can tell this gun is a Sig Sauer. The important stuff is made from steel, and the modular fire control system is designed in such a way that the slide operates with only steel-to-steel contact.


One of the primary design goals of the P320 pistol family was safety, both while in use and while being maintained.

Sig Sauer P320
The large triangular magazine release button is reversible to the other side and easy to reach and operate. author photo

Internally, there is a striker safety that blocks the striker from releasing and igniting the cartridge unless the trigger is fully depressed. This prevents the gun from firing if it’s dropped. A second internal system, a disconnect safety, prevents the pistol from firing if the slide is out of battery. That’s gun-speak for the slide not being completely locked into position. You definitely do not want to unleash 20,000 to 40,000 pounds per square inch of pressure unless everything is locked up tight! If you want even more security, you can order models of the P320 that have a tabbed trigger safety. The trigger on these models has a leaf in the center, which prevents any movement of the trigger unless the center leaf is depressed. The idea is that pressure from the sides alone won’t activate the trigger. You can also order your model so that it won’t fire if the magazine is not present.


When it comes time to take apart the 320 for cleaning or changing out some of the modular parts, you can do it without pressing the trigger. Some guns require a trigger press to release the striker tension before you can remove the slide, recoil spring, and barrel. With the Sig Sauer P320, all you have to do is pull the slide back, lock it in place with the slide stop lever, remove the magazine, and rotate the takedown lever. The pistol is designed not to come apart unless the magazine is out and slide locked back. Now the slide, barrel and spring will slip right off the front of the frame. No trigger manipulation is required.

Sig Sauer P320
Takedown for cleaning and maintenance is easy and does not require a trigger press, so it’s a very safe procedure. author photo

At the Range

The Sig Sauer P320 has a grip angle more like that of a 1911 pistol – closer to vertical. It’s not so severely angled as a Glock. I mention that because different shooters have different grip angle preferences. For me, the P320 points very naturally. If I close my eyes and raise the gun, it’ll be on target, with no need for alignment.

The gun I tested was chambered in .357 Sig. If you haven’t shot that before, it’s somewhat aggressive. While the construction and case dimensions are slightly different, it’s like a .40 S&W cartridge case necked down to accept a 9mm bullet so it looks a little bit like a stubby rifle cartridge. The whole point of it is that the extra case capacity drives the bullet a couple of hundred feet faster than a 9mm. It’s not uncommon for a .357 Sig bullet to exceed 1,400 feet per second. I mention all this to make the point that the round has snappy recoil, but I found the P320 easy to shoot, even with the sharp recoil. The grip on the P320 is far more rounded than that of a Glock, so I think there’s better contact with the hand, making the gun more controllable under heavy recoil.

Sig Sauer P320
All P320s have a Picatinny rail for attachment of lights or lasers. author photo

I did some fairly geeky accuracy testing in an informal head-to-head test against a brand new Sig Sauer P226 chambered in the exact same .357 Sig chambering. To take my aging eyesight out of the equation, because that would almost certainly foul up the results, I mounted a Bushnell Elite 3500 Handgun Scope on each gun using a UM Tactical rail-mounting adapter. The Bushnell offers variable 2-7x magnification, so I was able to get a perfect sight picture of my targets 25 yards down range.

I fired multiple five-shot groups for each type of ammo and averaged the results. I figured this approach was at least half-scientific and would give me a decent representation of which gun was technically more accurate. Guess what? The modern plastic modular P320 beat the old steel P226 warhorse.

Impressed, I continued to shoot a wide variety of .357 Sig ammo from the P320 and recorded average five-shot group size from the 25-yard distance mark:

Ammunition Bullet Weight Avg. 5-Shot Group Size @ 25 yds
Cor-Bon JHP 125-grain 2.04″
Doubletap Barnes TAC-XPD 80-grain 1.81″
Doubletap Controlled Expansion JHP 125-grain 1.82″
Doubletap FMJ Flat Point Match 147-grain 1.32″
Doubletap FMJ Fat Point Match 125-grain 1.51″
Doubletap Nosler JHP 125-grain 2.13″
Federal Premium Bonded Defense 125-grain 2.17″
Hornady Critical Defense 115-grain 2.19″
Remington UMC 125-grain 1.91″
Sig Sauer FMJ 125-grain 2.38″
Sig Sauer V-Crown JHP 125-grain 1.69″
Speer Gold Dot 125-grain 2.33″
Winchester PDX1 Defender 125-grain 2.32″

As you can see, this Sig Sauer P320 is an exceptionally accurate pistol. Plenty of guns will shoot groups less than three inches at 25 yards, but if I’ve tested one that regularly shoots groups smaller than two inches, I can’t remember when.

Sig Sauer P320
MSRP for the P320 ranges from $628 to $713. author photo

I expected the modularity to be the driving feature with this gun, so I was somewhat shocked at how well it performed, especially during accuracy testing. I actually called a contact at Sig to make sure my results weren’t skewed by something I wasn’t seeing. I couldn’t believe that this polymer striker-fired gun would be more accurate than the venerable all-steel P226. The response? “Yep, you’re correct – that was one of our design goals.”

MSRP for the P320 ranges from $628 to $713. Learn more and get the full specs here.