Everything You Need To Know About The Sig Sauer P320

The Sig P320 is one of the most popular pistols currently out there, rivaling the Glock 17/19, M&P9 and similar pistols in use in law enforcement and other official capacities, in competition, and in popularity with the shooting public. 

So, what is it that you should know about this gun if you didn't know anything? If you were thinking of getting one, why consider one? 

In this guide, we're going to give you a good idea of what the P320 is all about, what models are out there, and what makes it a good pistol. 

Sig P320 101

Sig P320

The Sig P320 is a polymer-framed, striker-fired pistol, made by Sig Sauer. 

Just like every other gun of the type, the gun has an accessory rail, a steel slide that's offered in compact (3.9 inch barrel) and full-size (4.7 inch barrel) versions, and it's fed from a double-stack (staggered column) magazine. 

Compact models hold 15+1 of 9mm, full-size models hold 17+1, and extended magazines increase capacity to 21+1. While other calibers are available via conversion kits from Sig Sauer, but aren't offered on most factory pistols. 

The heart of the gun is Sig Sauer's Fire Control Unit, a self-contained firing system including the trigger, trigger bar and the sear. The FCU can be taken out of the gun and swapped into a smaller or larger frame at the owner's discretion, so the gun is highly modular. 

For instance, you can swap the standard (medium) grip module for a small grip module for a slimmer grip, or a large grip module for shooters with larger hands. Caliber conversions are available as well for those interested. 

The safety system includes a firing pin block and a trigger bar that doesn't connect with the sear until the trigger begins to travel backward. The trigger does not include a tab safety or hinged/bifurcated trigger assembly; the passive safeties are fully internal. 

So, it's a modern pistol (polymer frame, striker-fired, double-stack magazine) with a firing system in a removable chassis.

The Sig P320 Is The Sequel To The Sig P250

The Sig P320 didn't come out of left field, as the gun is a modified Sig P250. In fact, most of the parts are the same.

The difference is the ignition system. The P250 was an internal hammer-fired, light DAO similar to a HK P30 whereas the Sig P320 is a conventional striker-fired design, with a firing pin/striker assembly that is fully cocked by the slide. The P250 - while not "bad" by any stretch - didn't exactly set the world on fire. 

While the modular frame system and easy caliber change was interesting, that didn't make endear the pistols to the shooting public as the factotum handguns the marketing materials said they were. While that's a neat feature, ultimately it comes down to whether the gun is a good shooter's pistol, and that's where the Sig P320 vs. P250 tips in favor of the P320. 

The gun-buying public had small love for the P250's trigger, which was longer and grittier due to being DAO. The gun was introduced in 2007, but Sig Sauer stopped adding any additional frames or caliber kits to their product line by 2009, and dropped it entirely by 2018. The Sig Sauer P320 was announced in 2014 to much fanfare, and soon replaced the P250, and - since the US military specifically requested a modular handgun design - was a natural fit for the XM17 pistol trials.

The P320 Frame And Grip Module System

So, to understand the gun a bit more, let's delve into the frame scheme. Like many other pistol designs such as the 1911, Glocks and more, the basic operating system is the same but it fits into a number of different frame sizes. The owner, of course, can swap the Fire Control Unit between frames and add slide/barrel assemblies.

Initially, Sig Sauer offered four frame sizes: Full, Compact, Carry and Subcompact.

The Full frame is the full meal deal service-size gun, with a 4.7-inch barrel and 17+1 capacity in 9mm.

The Compact and Carry frame use the same slide (with a 3.9-inch barrel) but the Carry frame is the same height as the full-size frame, accepting the same 17-round magazines. The Compact, of course, is a compact model that uses 15-round magazines.

The Subcompact slide housed a 3.6-inch barrel, and used a 12+1 magazine in the 9mm version.

Initially, all models were offered in 9mm, .40 S&W and .357 Sig, and within a year of the Sig P320's release, further variants were offered in .45 ACP. However, all calibers that are not 9mm proved less popular and aren't offered in production pistols though caliber change kits are still available.

In the fullness of time, the Subcompact models have been discontinued entirely and fewer Carry frame models are being offered. Each frame - Sig Sauer calls them "Grip Modules" - is also offered in sizes, similar to backstrap panels of other pistols. Each frame size is offered in Small, Medium and Large sizes, in case you prefer a smaller (or larger) grip size.

Initially, the gun was offered in 9mm, .40 S&W and .357 Sig. Large-frame .45 ACP models were offered as of 2015, but the caliber offerings have dwindled as fewer people are buying .40 S&W pistols and hardly anyone was buying .357 Sig pistols to begin with. However, part of the draw of the gun was it's modularity; you could swap calibers if you wanted.

The Caliber X Change kits include a grip module, slide assembly, barrel, recoil spring assembly, and one magazine. You just have to swap the FCU.

The P320 Becomes The M17 And M18

A Sig Sauer P320 variant was submitted for consideration in the XM17 Modular Handgun System competition, with some minor changes to meet the military's desired features in a handgun.

The frame hardware, such as the takedown screw, is slightly different, the steel parts in the gun have a PVD finish for more reliable operation in sandy conditions, and the frame is slightly different. The gun has a tan/FDE finish, optic cuts, an accessory rail, and ambidextrous thumb safeties.

The M17 is the full-size variant with a 4.7-in barrel and the M18 is the compact/carry model, with a 3.9-in barrel. However, both pistols accept the 17+1 flush and 21+1 extended magazines. Both pistols were adopted by the US Army, but the Air Force, Navy and US Marine Corps favor the M18.

The civilian market, of course, tends to follow LE/military purchases; we tend to buy what the professionals use. As a result, the P320 became hugely popular with the shooting public. While the M17/M18 variants weren't made available to the public at first, they are now.

However, besides the Nitron models and the M17/M18 pistols, Sig Sauer wasn't content to rest on their laurels.

P320 X Frame, SPECTRE, And Legion Models

Like the standard gun, what is now the X frame was developed for the P250 and has carried over…but with some additional features. If you think of the P320 frames like trim levels on a car, the X frame is the sport trim. If the standard P320 is a Honda Civic, the P320 X series are the Type R.

You get a different body kit, leatherette bucket seats, infotainment system, upgraded brakes and a tuning package for a little more horsepower and way better handling. While the changes aren't huge, the whole becomes a bit more than the sum of the parts.

On release, the X series includes Full, Compact and Carry models, but the Carry has been discontinued except for the Legion and SPECTRE trim packages. Other trim series such as the TACOPS have come and gone as well.

The standard guns are sometimes criticized for the grips, a trigger pull that's a little too long with a bit too much uptake, and not enough real estate under the beavertail. The X Series addresses those things.

The X Series changes the trigger from the curved trigger of the standard P320 to a flat blade. The frame is slimmer, with a deeper beavertail and trigger guard undercut for a higher, tighter grip on the gun, and the grip texturing is slightly more aggressive.

These changes make a difference; a lot of shooters find the X frame more ergonomic, and the trigger much improved by the flat blade.

Additionally, the slides are cut slightly differently and have slightly different cocking serrations. All X series slides are optics-ready, and you can order them with or without a RomeoZero optic and co-witness height sights.

However, X series/Legion/AXG pistols don't fit all P320 holsters, and use a different magazine due to the different frame, so bear that in mind.

The P320 X-VTAC, still in production at the time of this writing, is an X series full-size with a tan slide instead of black, and uses Sig Sauer VTAC sights instead of the standard Sig X-RAY sights.

The Legion series is basically the same, except that frame is stainless steel instead of polymer.

The SPECTRE series is a trim package, offered on multiple Sig Sauer pistols including the P320, P226, P365 and P365XL.

The X series SPECTRE models are made in the Sig custom shop. The grip module is laser-engraved with the SPECTRE grip texture. The slides are ported, and can be ordered with a Nitron or distressed black finish, and the barrel has a gold-colored TiN (titanium nitride) finish.

There's also the SPECTRE Comp model, which adds a compensator to the Full model.

Sig P320 AXG

The AXG series of the P320 is the luxury model. If the standard P320 is a Honda Civic, and the X Series is the Type R, the AXG is the Acura ILX.

The AXG, made in Sig Sauer's custom shop, uses a stainless steel frame, like the Legion series, but uses grip panels a la the P226. The slides come optics-ready, and both AXG models are offered on the Carry frame.

You can choose the Equinox model with Sig's Equinox finish and a flat trigger, or the P320 AXG Classic, which has the standard P320 trigger and Hogue walnut grips.

The AXG series are limited editions (get 'em while they last!) and come in a Negrini Custom Works case, with a challenge coin and a certificate of ownership.

What's So Great About The Sig P320?

The bog standard P320 Nitron models are solid workhorse pistols, on par with other modern service pistols. They do what they need to do if you do your job as a shooter.

The full-size is a capable service pistol, the compact is a very capable carry pistol. Solid working class guns for working class people. They aren't match pistols, and anyone out here pretending one is a Les Baer or something needs to stop it.

If you find it fits your preferences, it's a great gun! The truth is the big-name guns of this type are fairly uniform in size and features; there is no real "best" of them besides personal preference, and if the P320 is yours that's awesome.

If you wanted to get one as a base gun, you can also drag it through the various aftermarket parts makers' catalogs and build it up into whatever you wanted.

But…the conversation can change a little when it comes to the X series, Legion or AXG guns.

The premium trims improve the breed considerably, in terms of ergonomics, the trigger press, and other features like optics compatibility and more. There's less room for improvement besides perhaps a match-fit barrel or a match trigger.

So let's say you wanted a handgun that's about as improved as a handgun can be out of the box and ready for duty, competition, whatever you can think of. The X, Legion and AXG guns are and would be great choices.

Given also that X series pistols can easily be had for around $600…those guns in the P320 lineup are also a bargain, making them feature-rich pistols that don't break the bank.

So, that's what you need to know about the P320. It's one of the various poly-striker guns, and a decent example of one. It has a somewhat novel firing system. But once you start adding the optional extras...it becomes one of the best factory pistols you can get.

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Writer sam hoober