Sig Sauer P365 Parts 2 and 3

Sig Sauer P365 Parts 2 and 3

The smallest 9mm Pistol’s understudy

By Dennis Adler

The best features of the 9mm model are built into the CO2 version including the green front dot sight and white dot rear. On the 9mm model they are tritium night sights, but we have to live with traditional daylight sights, but still correct in appearance and extremely quick to put on target. Also note that the P365 bears no airgun markings anywhere on the slide or frame. Everything is on the underside in small type that almost blends into the black polymer frame. You can see the ambidextrous right hand thumb safety, Sig Sauer markings on the grips and frame along with the serial number inset. The only non-functional piece is the extractor (nothing to extract) which is deeply molded in to look like a functioning piece of the gun.

As someone who has carried handguns of all sizes for over 30 years it is hard to look at the Sig Sauer P365 and not be amazed at its size. I have carried .380s that are larger. And the .380 is an ideal place to start for comparison. Looking at this from a purely handgun perspective (with CO2 training guns in mind), one of the more popular .380s for concealed carry today is the Glock 42. I carried one for awhile and then reverted back to my custom built Ruger LCP. Why, because the Ruger (mine being the red trigger model) has a capacity of 7 rounds (6+1), the same as the Glock 42, but is smaller and more comfortable to carry.

About the smallest .380 pocket pistol is like the one I often carry, the skeletonized alloy red trigger model LCP, which has a 6+1 capacity.

The Ruger has a 2.75 inch barrel, the Glock a 3.25 inch barrel, so that accounts for some of the difference. But these are not for shooting targets; they are for saving your life in a close quarter confrontation, rarely beyond 21 feet and often as close as 10 feet or less. Barrel length isn’t going to matter too much. Matching CO2 models are ideal for training for this purpose. Many of you will never carry a centerfire pistol, or own one, but the overall purpose of CO2 models like the new Sig Sauer P365 is to offer that capability, as well as provide an air pistol for sport shooting. The size of the Sig falls into a category populated by smaller caliber handguns.

The Glock 42 is one of the most popular .380 models and comparatively small but still limited to 6+1 capacity. The measurement numbers 1 through 7 are 5.94 inches, 5.75 inches, 0.98 inches, 0.83 inches, 4.13 inches, 4.92 inches, and 2.40 inches. The Sig is smaller in most dimensions and is a 10+1 capacity 9mm pistol.
In comparison, the overall length and height of the P365 compared to the Glock is 5.8 inches and 4.5 inches (with the finger extension magazine). In width, the Sig is 1.0 inches at its widest with a slide width of 0.81 inches (compared to 0.83 inches for the Glock). The Sig is a little longer by 0.05 inches, 0.37 inches taller, but again is a 9mm with a 10+1 capacity compared to a .380 with a 6+1 capacity. Seems like Sig Sauer has made the case.

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Today’s modern personal defense ammunition (Federal Premium Personal Defense and Sig Sauer Elite Performance V-Crown, as an example) make the .380 a very effective caliber, but still not as effective for self defense as a comparable 9mm round. Now, Sig Sauer makes some excellent .380 pistols in their P238 series (similar in size and operation to a Colt Mustang .380) as well as the P938 models in 9mm (single stack, 6-round magazines), so they know how important it is to build a 9mm that is as close as possible to the size of a .380 for superior personal defense use.

Sig Sauer’s Micro-Compact .380, the P238 is about the same size as a Colt Mustang 380 and is based on that 1911-style design with a 6-round single stack magazine.
Just slightly larger than the .380 ACP Sig model, the 9mm P938 is again based on the Colt design with a 6-round single stack magazine. This is a smaller gun than the new P365, but with less capacity. It is also a hammer-fired SAO. It is an excellent gun, but technically outdated compared to the striker-fired, polymer frame, high-capacity P365.

When you can have a 9mm that is barely larger than a .380, and I am talking very little difference overall, you would probably select the 9mm over the smaller caliber pistol, even if it had the same capacity. But let’s add some Sig Sauer magic and give that gun a 10+1 capacity. Add impressive sights, ease of handling, ambidextrous manual safeties, light carry weight, a contoured frame and impressive grip design and magazine combination that allows a firm grasp, and you have a multiple Handgun of the Year winner.

Sig Sauer’s SIG AIR Division knew the P365 was going to be an out of the gate winner for CCW and backup pistol use across the board, groundbreaking designs that work tend to go that way, and they wanted to be able to offer a matching CO2 model for training and for CO2 air pistol enthusiasts who want a blowback action pistol that is identical to its centerfire counterpart; a CO2 powered, .177 caliber understudy, and that is exactly what we are talking about.

The CO2 model has the exact same lines as the 9mm including the front slide serrations. Even the contours of the barrel in the slide ejection port are the same, which you don’t find even in some more expensive blowback action CO2 models. They’re close but not exact. Also note how trim and well-shaped the thumb safeties and slide release are to the side of the frame, yet they are very easy to work. The entire gun is angled and tapered to minimize mass and aid in easy re-holstering. The CO2 model fits all P365 holsters.

How does this play out in centerfire guns? Consider 10+1 capacity in 9mm with an overall length of 5.8 inches, a width of 1-inch, a height of 4.3 inches (with the flush magazine, 4.5 inches with finger extension) and a weight of 17.8 ounces empty. The tradeoff in weight for having a 9mm is negligible compared to the .380 ACP Glock (15.87 ounces vs. 17.8 ounces), and almost half a pound compared to the little Ruger .380 ACP at 10.6 ounces, which is hard to beat. But in overall size, the differences are more revealing as shown in the photos; 5.94 inches for the Glock vs. 5.8 inches for the P365 (smaller) and 5.17 inches for the Ruger. For height, the Ruger is smallest at 3.71 inches but the Glock at 4.13 inches vs. the Sig at 4.3 inches is pretty close. The Sig is the widest at a mere 1.0 inches (at its widest point) compared to the Glock at 0.98 inches. The Ruger is smaller overall, but is a .380. And as for CO2 counterparts for training or sport shooting with BBs, there are no Glock 42 or Ruger LCP air pistols. Sig Sauer has scored bullseyes in both the centerfire and CO2 categories with the P365.

The interesting part of the 9mm model, in terms of capacity, is the shape of the magazine and its dual stack design allowing 10 rounds instead of a more typical 6 rounds in a single stack 9mm magazine. The same shape is used for the CO2 model which is barely taller than the CO2 it holds. The design is unique for an air pistol, as is how it works with the firing system.

How did they do that?  

SIG AIR knew the production schedule for the P365 9mm model and wanted to have a matching 1:1 CO2 model ready. Considering the unique design of the centerfire pistol, and its compact double stack magazine, allowing the 10+1 capacity, the typical solutions for making an air pistol would not allow a 1:1 CO2 model. There is also an extended capacity 9mm mag for the P365 that increases the length of the grip and holds 12 rounds, and that is the reason why the CO2 model loads 12 BBs and not 10. But SIG AIR did not want to compromise the exterior dimensions by pulling the old extended capacity magazine trick.

The cup in the seating screw is shallow to minimize size, and as you can see, the CO2 goes from the base of the magazine all the way to the valve when loaded. There is zero waste of space. But there is more to it than size alone.

To put the designs in perspective, you have to start with the idea that the mechanisms in a centerfire or rimfire pistol utilizing a firing pin to strike a cartridge primer, ignite the gun powder in the shell and send the bullet down the barrel cannot be duplicated in a CO2 pistol, because the gun itself, through the CO2 system, has to provide the ignition to propel the BB or pellet down the barrel. CO2 mechanisms take up space in the frame and within the CO2 BB magazine. In every case a larger handgun like a 1911 allows this to work within the same size pistol. As guns get smaller the problem of making everything fit increases exponentially. The solution for most is to use extended capacity-style magazines that will allow more room for the CO2 mechanism. And that’s how it has been done up to this point, except for some older designs like the Umarex Walther PPK/S, where the grip frame is just a little longer than the centerfire pistol’s.  With few exceptions this has also required the use of a stick magazine. To do what SIG AIR has done in building a 1:1 CO2 version of the P365 9mm pistol required a clean sheet of paper and 18 months of design work to rethink how a blowback action CO2 mechanism and self-contained CO2 BB magazine could be scaled down to fit, and still use a standard 12 gr. CO2 cartridge.

In the Sig Sauer “has another first” category, the magazine interlocks with the back of the barrel. Looking down on the magazine you may see the small spring-loaded BB stop that protrudes in front of the follower. With BBs loaded, this keeps the top round from falling out.

SIG AIR’s Product Manager Dani Navickas explains that “Sig likes to challenge their R&D engineers, so it was actually a challenge to the R&D team to completely replicate the P365 in 1:1 scale so it would be a great training tool. It had to be an equal.”

The quick fix to making a CO2 pistol this compact was to use a smaller 8 gr. CO2 cylinder, but the goal was to end up with a design that used a full size 12 gr. CO2. “The 12 gr. [cylinder] scale is basically the size of the P365 CO2 BB magazine, so everything had to be designed around that. This was really breaking new ground,” says Navickas. She explains that in order to make it work “…you have to start shaving off every fraction of an inch and designing parts that can do the same job but take up less space. The valve for the magazine is unique in its design and is at a slight angle to save a little extra space. The interface of the barrel breech with the BB magazine is a completely different design than anyone has ever used.” Looking at the gun up close you can see they actually lock together, and the spring-loaded BB stop, which prevents BBs from falling forward until the magazine is loaded into the pistol, is pushed out of the way by the back of the barrel as the magazine locks into place.

When the magazine is inserted into the grip, the back of the barrel pushes the BB stop down, allowing the BBs to align with the barrel breech, which locks into the magazine. The barrel never moves when the gun is fired and remains in contact with the magazine at all times.

The new 9mm and CO2 P365 design is based on the larger P320, while Sig Sauer’s earlier Micro-Compact 9mm and .380 ACP models (P938 and P238) were based on the old Colt Mustang .380 SAO, hammer-fired, design, itself derived from the Colt Model 1911.

The firing system for the P365 CO2 model is integrated into the frame (a similar concept to the recent P320/M17 ASP pellet model), and this utilizes an internal striker-like mechanism to actuate the valve and release the CO2 when the trigger is pulled. The P365 CO2 design acts like a striker fired pistol. Striker style air pistols actually use a small internal hammer to hit the release valve so they are still hammer fired, but the SIG AIR design does not. It is “closer to a striker firing system than a hammer firing system” and it is also smaller, again working with the rest of the firing system and CO2 BB magazine design to maintain the correct centerfire pistol dimensions.

In a typical blowback action CO2 pistol with a short-recoil, locked-breech, tilting-barrel design, when the slide comes back the barrel tilts up. It does with the 9mm model but not on the CO2 pistol because the barrel is solidly fixed to the frame (like the barrel on a Walther PPK, for example). You can also see that slide locks back short of its full blowback action movement (0.8125 inches from the back of the beavertail) which approximates the 9mm slide. It locks up short (0.437 inches from the back of the beavertail) on an empty magazine due to the barrel and magazine interface.

There is one minor concession to scaling down the internal mechanisms, it requires a fixed barrel rather than a short-recoil, locked-breech, tilting-barrel design like the centerfire model and other high end blowback action CO2 pistols, and this is evident when the slide locks back because the barrel remains level. This also precludes field stripping the gun, though SIG AIR says that the gun can be disassembled but not the same way as the centerfire pistol. There is no mention of this in the instruction book and SIG AIR does not recommend taking the CO2 model apart. “To meet the R&D goals, and have a self-contained CO2 BB magazine, it was more important to get the handling, operating features and size correct, than to be able to fieldstrip the gun,” explains Ed Schultz, SIG AIR’s Engineering Manager.

The CO2 model still uses a guide rod and recoil spring and the .177 caliber muzzle is recessed 0.25 inches from the 9mm diameter barrel muzzle.

The blowback travel of the slide is very close to the centerfire pistol’s but when the slide locks open on the empty magazine, or if you manually lock it open, it rests further forward on the frame due to the close interface and locking mechanism of the barrel and magazine. “There is a fun factor to being able to fieldstrip a CO2 model,” admits Schultz, “but for the P365, it isn’t so much a tradeoff as it is necessary to get the external dimensions right and have a self-contained CO2 BB magazine that is barely larger than the CO2 cartridge it holds.” This is the smallest blowback action air pistol there is. By any measure of achievement, SIG AIR’s R&D team met the challenge.

In Part 4 we will begin to look at holstering the CO2 model which fits all P365 holsters (and the magazines fit the magazine pouches) like this set from Galco, the Stinger Belt Holster and SMC Single Magazine Case.


In Part 4 we will begin velocity and accuracy testing and comparisons with the actual 9mm model.

A word about safety

Blowback action airguns provide the look, feel and operation of their cartridge-firing counterparts and this is one reason why they have become so popular. Airguns in general all look like guns, blowback action models more so, and it is important to remember that the vast majority of people can’t tell an airgun from a cartridge gun. Never brandish an airgun in public. Always, and I can never stress this enough, always treat an airgun as you would a cartridge gun. The same manual of operation and safety should always apply.

1 thought on “Sig Sauer P365 Parts 2 and 3”

  1. The 380 like your Ruger and my Colt Mustang Pocketlite are being relegated to the job formerly done by a 25 acp Pocket Pistol, backup or carrying when nothing else fits your dress or lifestyle.Pistols like the Walther Ppk, Ppk/s are relegated to the historical status. 21-24 ounce blowback 380 just not in the running for carry pistols. I suspect the PpK series like the classic Browning High Power will soon be discontinued, maybe replaced by a similar looking polymer striker fired version version weighing 13-14 ounces. Glock is in trouble with their competition to the Sig. The 26 is chubbier , the 43 holds only 6 rounds and the newX extended grip version is a pathetic attempt to respond to the Sig. My bet is Glock will need a thinner version of the 26 to be competitive.. Didn’t thinkI would want a polymer pistol, but I picked up a Glock 19 to pair with my Ruger PC9 Carbine. Was waiting for the Sig with ambi safety and now it is here. Like the idea of a pistol you drop in a pocket to have a safety, also like that you can unload with the safety engaged. Anyone picking up the 9 mm version should have the co2 version. Would have like velocity in the 330-350fps range, but the barely 300 will make it a 7 yard practice pistol. Sig still has to be admired for what they have done here with this little pistol. Who dares, wins

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