Modularity is all the rage these days. Thanks to the U.S. Army’s XM17 pistol contract, it’s been at the forefront of the firearms world for some time now. The biggest component of this request for manufacturers was for a pistol that could easily be configured and reconfigured to handle several different uses. Sounds like a good idea, right? One serialized “module” that can be adapted with various frames, slides, barrels.

Military and law enforcement personnel have been asking for modularity like this for years—anything that makes it easy for an armorer to fit different users and/or different missions without issuing separate guns. Having been a police armorer, I can tell you that this concept certainly has some value. Rather than issue a different pistol for detectives, tactical units or even undercover assignments, you just swap all the parts, using the same internals as needed. Keep a few trigger modules around, and if a pistol goes down, you can swap it out while you make repairs. What if you want to change calibers or grip sizes? Sounds pretty slick if it works—and the Sig P320 system works.

Everything P320

I tested the Sig P320 when it was initially introduced in 2014, and it quickly became one of my favorite pistols. Its accuracy was excellent. It worked every time. My test pistol from 2014 is still in the hands of a colleague, and it’s just as accurate and reliable after sending thousands of rounds downrange. The only modifications were an Apex Tactical flat trigger and Trijicon HD sights. In the case of one very intensive class, the pistol digested over 2,000 rounds in a week without a single malfunction.

Sig Sauer’s P320 is now available in 11 different configurations, ranging from the Subcompact with a 3.6-inch barrel to Full-Size models using 4.7-inch barrels. Every model has SIGLITE night sights and a Picatinny rail for accessories (aside from the Subcompact). The RX models even come with ROMEO1 reflex sights. The TACOPS Carry model sports a threaded barrel for suppressor use. Sig’s latest P320 design, the X-Five, has a 5-inch barrel and a frame similar in shape to the company’s aluminum Elite frames. Of course, with each variant, three different frame sizes are available. The guns come with “medium” grip modules installed, but you can order smaller or larger versions in black, olive drab or Flat Dark Earth for $44.

Conversion Kits

The Sig P320 trigger mechanism fits in all of these variants, and you can remove it and reinstall it without tools, in the field, in very short order. Conversions kits consisting of a complete slide assembly (including a barrel and return spring), a new frame and a magazine are available in every size. For chamberings, you can choose between the 9mm, .357 SIG and .40 S&W; each is $407. Higher-capacity magazines (as high as 21 rounds in 9mm) will fit any of the smaller grip modules. In short, it’s possible to pretty much mix and match, as long as the slide is the proper length for your chosen grip frame, for real modularity.

Test Models

In 2014, I tested the Sig P320 in Compact and Full-Size guises. This time around, I got my hands on a P320 RX Compact. I’ve grown fond of reflex sights for carry, so it seemed like a good choice. And you can’t beat its price at $1,040 for what’s included. My only addition was a flat trigger from Apex Tactical. I then altered one of my AIWB holsters to fit the included ROMEO1 sight and put the system to work after some brief testing.

Next, I acquired a Full-Size conversion kit and a set of Sig’s X-Ray day/night sights. I’ve run these sights on a couple of Legion pistols, and they are now among my favorites. For OWB carry and competition. I picked up a Phantom holster from Raven Concealment Systems. This rig is light, fits tight to the body, and every P320 configuration I tested fit in it. The plan was to use the Full-Size pistol for duty-style practice along with tactical classes or competing in IDPA matches, and carry the RX Compact. The trigger’s factory-specified pull weight should work for most police policy requirements and service auto competitive divisions.

Born To Run

Finally, I obtained an X-Five Full-Size kit—perfect for Limited division competitions as well as 3-Gun. This grip module has a deeply undercut triggerguard, a higher backstrap and an extended beavertail. A grip weight is also included for better balance, but it can be removed if needed. The slide sports a fiber-optic front sight as well as an adjustable rear sight that can be removed and replaced with a ROMEO1 optic if needed. The magazine well funnel isn’t too obtrusive, and it can also be removed easily.

The 5-inch bull barrel and lightened slide make the Sig P320 X-Five Full-Size both fast and accurate. The large controls make it easy to reload the pistol’s extended 21-round magazines. But maybe the best feature is the flat trigger, which is tuned to a very crisp 4 pounds.

Switching Things Up

Swapping parts around on this system is incredibly simple. Remove the magazine, make sure the pistol is completely empty, lock the slide to the rear and push the slide lock lever all the way forward. Release the slide and remove it (you do not have to press the trigger). Now remove the slide locking lever, and the trigger mechanism will come right out. Reverse this process to put everything back together again. It’s that simple.

As an armorer, you can change entire grip sizes in a couple minutes, and the operative term here is “grip.” It’s not just a backstrap change—the entire module is matched in size. Moving to the small grip module on a P320 Compact for one of my customers was a true game-changer. Injuries he sustainted from an accident made this the only pistol of this size he could comfortably grasp.

Need to work on the trigger mechanism? No more fiddling with tiny parts inside the frame. I would take the Full-Size variant apart to clean it after training; reassembling it as a Compact for carry was quick and easy. It may not be everyone’s cup of tea, but it works. For someone like me who goes back and forth on all kinds of projects, this setup saves time and money.

Trigger Time

The Compact variant wasn’t new to me, but the ROMEO1 reflex sight was, and it worked just fine. It’s easy to adjust and is clear with an adjustable output level. You can also switch out its battery without removing the sight. The SIGLITE sights co-witness in the bottom of the ROMEO1’s window. With this gun, it was easy to hit 6-inch plates at 30 yards with ease, even single-handed. This is where a reflex sight really shines for me, and the RX Compact worked very well.

Then I removed the trigger mechanism and installed it in the Full-Size grip and matching slide, which provided equally accurate results. And with this setup, I installed a SureFire X400 so I could use one of the company’s MasterFire holsters, making it just about perfect for tactical deployments. Configured this way, the P320 remains one of the most accurate and reliable polymer-framed pistols I’ve ever used, and I’ve already run this variant at a couple events.

Shooting the P320 X-Five is quite pleasant. It’s far more accurate than my capabilities will allow. It shoots so softly that you’ll wonder if the gun actually fired. The fiber-optic front sight pops out at you in sunlight, and the adjustable rear sight allowed me to tune the gun for some reloads.

I ran the X-Five through a number of IPSC-style drills, and its performance rivaled that of my $4,000 high-capacity 1911. Its trigger is noticeably lighter and measured a tad over 4 pounds instead of the standard model’s 5.5 pounds. The reset is short and quick; I’m just not sure it gets much better than this.

Mod To The Max

If you can buy separate pistols, more power to you, but many cannot, making modularity useful. After running various P320 configurations, I would start with the X-Five Full-Size pistol—its trigger is that good. I moved it in and out of all my various grip modules, and it worked perfectly every time. Pick up the conversion kit you prefer (Subcompact, Compact, Full-Size, etc.) and swap the trigger in and out. If you compete, set it up for the match, then swap things around for everyday carry. Add other conversions as needed, including different calibers.

To carry two guns on duty or concealed, start with a Compact and a Full-Size and pick up a Subcompact conversion kit. Carry the Compact off-duty, but switch to the Subcompact setup for uniformed work. Your Full-Size is pistol one; the Subcompact is a backup with interchangeable magazines. If you compete using 9mm rounds but prefer (or are required) to use the .40 S&W or .357 SIG for duty, for example, pick up the X-Five and a .40-caliber conversion kit. Use the standard grip frame in .40 S&W if you must, or just swap out the slide and magazines and you are set while still getting the excellent trigger of the match-ready X-Five. It really is pretty impressive how much you can mix and match with this system.

Final Thoughts

In the end, modularity like this isn’t for everyone, but it’s just about perfect for me since I can use the same basic setup for concealed carry, duty and competition—all with the same trigger mechanism. Having been on trips where I attended three different training schools, the P320 can serve as a primary or secondary pistol, even a dedicated competition gun, often using the same holster.

Sig Sauer is offering more P320 options with each passing year. My guess is that winning the U.S. Army’s XM17 contract will only help improve on that. Modularity may be the “word of the day” in the industry, but the Sig P320 meets that definition as well as any, and better than most. Make sure you check it out.

Sig P320 Full-Size

  • Caliber: 9mm
  • Barrel: 4.7 inches
  • OA Length: 8 inches
  • Weight: 29.5 ounces (empty)
  • Grip: Polymer
  • Sights: SIGLITE night
  • Action: Striker-fired
  • Finish: Matte black
  • Capacity: 17+1
  • MSRP: $679

Sig P320 RX Compact

  • Caliber: 9mm
  • Barrel: 3.9 inches
  • OA Length: 7.2 inches
  • Weight: 25.8 ounces (empty)
  • Grip: Polymer
  • Sights: SIGLITE night, ROMEO1
  • Action: Striker-fired
  • Finish: Matte black
  • Capacity: 15+1
  • MSRP: $1,040

Sig P320 X-Five Full-Size

  • Caliber: 9mm
  • Barrel: 5 inches
  • OA Length: 8.5 inches
  • Weight: 35.6 ounces (empty)
  • Grip: Polymer
  • Sights: Fiber-optic front, adjustable rear
  • Action: Striker-fired
  • Finish: Matte black
  • Capacity: 21+1
  • MSRP: $1,005

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This article was originally published in the February/March 2018 issue of “Tactical Weapons.” To order a copy and subscribe, visit

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