M17 Reboot Part 1

M17 Reboot Part 1

Sig Sauer ups its game with optics

By Dennis Adler

The Sig Sauer P320/M17 ASP is the CO2 pistol that broke the barrier between BB and pellet pistols with the first self-contained CO2 pellet magazine. It is not a perfect design in overall operation, but it is a 1:1 gun for exterior appearance and basic handling. And as Sig Sauer’s Sig Air Division intended, it is an ideal training substitute for its 9mm counterpart. It is also the first CO2 pellet model to employ in its original design a removable optics plate. And that is where we left the M17 almost a year ago waiting for the next step. That time has come.

Sig Sauer is starting from a position of strength with the P320/M17 ASP, because it is still the only blowback action CO2 pellet pistol on the market with a self-contained CO2 pellet magazine, and it is also the only CO2 version of the exact pistol being carried today as the new standard issue U.S. military sidearm. To be fair, there are other handguns in use by U.S. military with CO2 counterparts, and the Marine Corps are opting for Sig’s compact M18 version, (which is not yet offered as a CO2 model, only Air Soft), but the majority of U.S. service branches are already carrying or will be carrying the M17. This is not news and the CO2 version has already proven itself, walking away with 2018’s Replica Air Pistol of the Year title. Even so, Sig Air knew there was still work to be done on the M17 ASP and has not rested on its laurels. This announcement is late but the option that the P320/M17 ASP needed most, the slide optics mount and red dot sight are finally here, and here is where we begin, with a look back at the CO2 model and where this new feature will take it.

Recapping the P320/M17 ASP

The role of the M17, as both a military pistol and as a blowback action CO2 pellet-firing air pistol, is very different than that of earlier Sig Sauer CO2 models because, although based on the P320 ASP, the M17 is an almost entirely new gun and there are noteworthy differences in both the centerfire and CO2 models compared to the P320, beginning with safeties. The P320 centerfire pistols do not have them. The Sig Sauer P320 ASP CO2 model, in complying with air pistol safety requirements, has an added manual safety on the left side of the frame, but technically a P320 doesn’t have one. The centerfire M17 uses an ambidextrous thumb safety, so that issue is eliminated with the CO2 model, which is nearly 100 percent accurate (externally), to its centerfire counterpart.

The little details give away the CO2 model but you have to look for them, they don’t scream air pistol. What’s different? No extractor at the back of the slide, no serial number plate for the removable fire control housing (because the CO2 model doesn’t have one), and the trigger angle is further forward. As a training gun for the 9mm model it checks a lot of boxes just the same for weight, balance in the hand, and basic handling from holster to the firing line.

The slide release on the P320 ASP was an accurate looking but inert component since the slide did not lock back. This has remained the same on the M17 ASP because even with its advanced CO2 pellet magazine design there is no follower with a belt-driven magazine, and thus no way for the slide to lock open when it is empty; its like pulling the trigger on an empty revolver. The slide on the M17 CO2 model cannot lock open even manually (although technically it could have been done with the slide release, there wouldn’t have been any actual purpose). On the other hand, the disassembly lever on the M17 ASP is a fully functioning take down lever, and unlike any previous Sig Sauer pellet model, the M17 ASP can be field stripped, though not the same as the centerfire gun. Taking the air pistol apart is where a great deal of the CO2 pellet magazine and its interface with the firing system are actually revealed.

The white dot sights on the CO2 model (right) are a little larger but the ones on the 9mm are SigLite night sights. The rear of the slide as it relates to the rails, frame and slide cap, and of course, the back of the extractor (which is missing on the CO2 model) are other slight tells, but pick up the M17 ASP and the feeling in the hand is about the same as the 9mm.

Sig Sauer’s design for the M17 air pistol is (still) as unique as its approach to the centerfire P320/M17 models. The 9mm models are a modular design that permits moving the fire control housing (the firing mechanism and trigger which are the actual serial numbered parts of the gun) from one frame to another thereby allowing the size of the gun to be changed from a full-size duty pistol down to a compact carry pistol. You can even change magazine capacities, barrels and calibers, and grip profiles for different users. The M17 CO2 model is a lot simpler; it is a dedicated 4.5mm pellet firing duty-sized pistol equal in dimensions to the M17 military pistol with extended capacity magazine. The 9mm magazine holds 21 rounds, for the ASP model the extended capacity rotary magazine holds 20 pellets and, of course, the CO2.

The M17 Magazine

This is the engineering marvel of the M17, a first-of-it-s-kind self-contained CO2 pellet magazine with a 20-round rotary fed “clip” and I know we don’t call magazines clips, but in this case it is a clip that locks into the magazine. It’s also the official term Sig Sauer has given to the modular pellet-loading device for the M17 magazine.

Loading the CO2 into the large main section uses a long lever that folds down away from the back of the magazine housing. This is similar in operation to the loading system Sig Sauer developed for the P226 ASP, which had a folding backstrap panel to accomplish the loading and seating of the CO2 cartridge in one motion. With the M17 magazine, once the lever is lowered the CO2 is inserted. You then raise the lever and squeeze it closed against the back of the magazine and in one move the CO2 is locked, raised into place, pierced and sealed with the housing that fits into the pistol’s grip frame. This is part 1 of the 2-step loading process. The pellets load into a compact version of the P320 rotary magazine; once loaded, the clip drops into a channel and locks into place. The CO2 and pellet clip are now one piece within the magazine and ready to load into the M17. At this point you have one the most authentic looking CO2 versions of a modern military pistol. The system works, the gun is reasonably accurate for its design, and it fits the description of a CO2 powered training aid. This is what led the M17 ASP to win 2018’s top air pistol award.

The innovative CO2 pellet magazine design allows a single mag to hold both, a first for an air pistol. It is also easy to load pellets and CO2 with the Sig’s design. Sig even has spare clips to reload when using a single magazine. But at the price of spare compete mags, it makes sense to have at least two extra and ready for learning quick magazine changes and tactical reloads. The only problem is that the CO2 pellet magazines do not fit a standard M17 mag pouch. They do, however, fit in the extended mag pouches that come with most tactical vests. An M17 CO2 dual mag pouch would be a great aftermarket product!
From any angle the air pistol and 9mm look virtually identical. But the real story for both is on the inside.

The internal design of the CO2 version is different from most pellet-firing CO2 pistols, and even the Sig Sauer P320 ASP model. Unlike the majority of blowback action CO2 semi-autos the slide for the M17 houses nothing but a locking block and firing pin (or rather the CO2 version of one); the rest of the CO2 action is housed in the frame. And while the M17 CO2 pistol isn’t a modular design, the concept behind its layout is still based on that principle.

Sig Air did go the extra mile with the M17 to make it a gun that fieldstrips similarly to the 9mm model. The rifled CO2 barrel and recoil spring can also be removed but it really serves no purpose. The portion of the M17 ASP attached to the frame is the CO2 firing system and it fits into the injection molded frame much like the fire control housing on the 9mm, which fits inside the frame.

Once you remove the slide, the M17 ASP is an open book; remove the magazine and look up inside the grip and you have a clear view of the internal operating system, the opening for the rotary pellet magazine to fit in between the CO2 valve and the forcing cone at the back of the barrel housing, and the connecting valve that fits into the magazine’s CO2 chamber. All very straightforward in application and totally dependent upon the modular CO2 pellet magazine to operate.

It was obvious from the beginning that the top rear portion of the slide looked like a separate piece, but when the CO2 model came out it had no apparent reason other than it matched the look of the centerfire gun. Of course, Sig Sauer already had a plan for this piece that was, in fact, separate and removable just like on the 9mm guns.
Here you can see how the entire firing system fits inside the injection molded frame. The inside of the slide is pretty much a shell except for the long U catch that secures it to the frame, the black plastic slide cap at the rear, and those two curious screws at the back we told you not to remove.

In 2019 the Sig Air Division embarked on the next step of the gun’s evolution and had planned to take that step by year’s end. A step that would have given the air pistol added parity with its centerfire counterpart, which has a removable optics base built into the slide that can be replaced with any of several mounting plates to fit red dot reflex sights. This was something I noted back in 2019 and had even hinted at in 2018 because it was obvious that when you took the slide off and looked inside, there were screws running into the top of it. I said yes, but don’t unscrew them. Sig Air said yes but don’t unscrew them and I hope that those of you with an M17 ASP didn’t unscrew them. The reason was simple; the black section at the rear of the slide and the rear sight attached to it will come off. But here was the thing; the same replacement mounting plates that fit the centerfire M17 wouldn’t fit the CO2 version. Sig Air had another reason, too, and a very logical one. Even if the plates had fit, the reflex sights that would fit the 9mm model cost way too much to purchase for an air pistol. I might have done it (actually I already had the reflex sight that fits one of the M17 mounting plates) but the majority of airgun owners wouldn’t have done it. Why tease? I guess it ended up being a tease because the product I had hinted at last year got delayed and then world went sideways and it has taken until now to get a perfect Sig Air mounting plate and red dot reflex sight to market, and complete the M17 ASP package.

As soon as you have one of these you can get out your screwdriver…The Sig Air reflex sight and mount will be available within the week and I will post the link as soon as they hit the shelves.

In Part 2 we start removing screws and un-boxing the new Sig Air M17/M18 Low Profile Reflex Sight.  

One thought on “M17 Reboot Part 1

  1. I have had this pistol for nearly a year and have shot 1000s of pellets through it. It has worked well although now both mags are a bit tired. One is unusable and one only seals when in the pistol. Tried various methods of sealing with no joy. I suspect with use the spring and washer need replacement but spares are hard to come by. Better than any other mag with gas in the mag such as KCW 1911 or sig 365(aweful). I improved accuracy with a plastic insert as there was a lot of play in the slide (see youtube) .You do occasionally get pellets stuck in the breech (I use excite econ) but the drill is to release the mag and drag it out for a quick clear. Along with my cowboy legends this has been my most enjoyable air weapon. Looking forward to fitting my new sight!!!


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