Sig Air M17 ProForce airsoft pistol: Part 2

by Tom Gaylord
Writing as B.B. Pelletier

Sig M17 Proforce airsoft pistol
Sig M17 ProForce airsoft pistol.

Part 1

This report covers:

  • 21 rounds
  • Loading the magazine
  • 0.20-gram airsoft BBs
  • CO2
  • Green gas
  • ProForce technology
  • Velocity
  • Sig 0.20-gram BBs on CO2
  • TSD 0.20-gram BBs on CO2
  • 0.25-gram Valkers Accelerator BBs on CO2
  • Discussion
  • Blowback
  • Shot count
  • Switch to green gas
  • Sig 0.20-gram BBs on green gas
  • TSD 0.20-gram BBs on green gas
  • 0.25-gram Valkers Accelerator BBs on green gas
  • Shot count on green gas
  • Trigger pull
  • Rapid fire
  • Summary

Today we look at the velocity of the new Sig ProForce M17 airsoft gun. In Part One I was confused and wrote that Sig also made an airsoft gun that did not use both green gas and CO2 interchangeably, but that was incorrect. The ProForce line is currently their only airsoft line and this ProForce M17 pistol is the only airsoft version of the M17 that they make. The pistol I am testing can use either CO2 or green gas as a propellant. Each gas takes its own dedicated magazine. The pistol comes with the CO2 magazine and the green gas magazine is available as an option, so I asked Sig to please send a green gas mag as well, and they did. I will test both gasses for you today.

21 rounds

I mentioned that this airsoft pistol holds 21 plastic airsoft balls that the industry calls BBs. Then I mentioned that my personal 9mm Sig P320 M17 firearm magazine holds 17 rounds. That’s because I got the short magazine that terminates at the bottom of the grip. I did not buy the optional extended 21-shot magazine. A reader mentioned that the military sidearm uses the extended mag, which is correct. Then another reader said Sig should sell the airsoft gun with the same number of rounds as the firearm, and he keyed in on my short mag and 17 rounds. Sig has made the airsoft pistol to copy the military sidearm, so 21 rounds is exactly right.

Sig M17 ProForce magazine 1
The 21-shot magazine arranges the BBs in a double stack. BBs are fed from the top one at a time.

Loading the magazine

The spring-loaded follower must be held down to load the magazine. This is true for both the CO2 and green gas mags. There is no lock to hold that follower down, so one hand is always involved, holding it down so the BBs can be loaded.

Sig M17 ProForce magazine 2
The magazine follower has to be held down manually to load.

0.20-gram airsoft BBs

The manual does not specify what weight of 6mm airsoft BB to use, but the box the gun comes in has a graphic on the back that gives the velocity for a 0.20-gram BB. So, that’s the weight Sig recommends. They also sent me a small bag of plastic BBs for this test and when I weighed them on a sensitive powder scale they were consistently 0.20-grams. But, because the pistol can use the two different gasses, there is more to this. I will discuss that now.


Carbon dioxide, or CO2 as we refer to it, has a vapor pressure of 853 pounds per square inch at 70 degrees F. It is a gas at 70 degrees F. but its pressure varies as the temperature goes up or down. That’s why on colder days CO2 doesn’t push pellets (or airsoft BBs) as fast as it does when things are warmer.

An airsoft BB is quite light in relation to its size. The BBs are 6mm in diameter which is nominally 0.236-inches, so they are larger in diameter than a .22 caliber ball. But, at 0.20-grams, they only weigh 3.09 grains. That’s light.

Green gas

Driving a light projectile with high-pressure gas is not easy to control. That’s why you haven’t seen many airsoft guns running on CO2 in the past. The airsoft industry has made wider use of propane — another gas that is temperature-dependent. The industry calls it green gas, and it contains a small amount of silicone oil as a lubricant for the valve train inside the gun. And the, “Is green gas really propane?” debate has raged on for many years and will probably never be resolved. Look it up.

At 70 degrees F. green gas generates about 115 psi of vapor pressure. To push an airsoft BB at that pressure the valve has to open easier and remain open longer to pass more gas, so the valve return spring is much lighter and the gas passageway is larger to accommodate the difference.

ProForce technology

For the ProForce M17 pistol to work, the same hammer blow has to open both a CO2 valve operating on 850 psi and a green gas valve that works with 115 psi. That is a hat trick in the airsoft world. It has been done before, but it isn’t popular, for the reason I have just presented.


Given what I just said about pressure you probably realize that when the gun runs on CO2 the velocity will be higher than when it runs on green gas. On the back of the Sig box we are told to expect velocities for 0.20-gram BBs of up to 410 f.p.s. on CO2 and 320 f.p.s. when we use green gas. Let’s now test the pistol and see what it actually delivers. CO2 will be first.

Sig 0.20-gram BBs on CO2

On CO2 the Sig 0.20-gram BBs averaged 423 f.p.s. for 10 shots. So they are above the advertised maximum. They ranged from a low of 411 f.p.s. to a high of 432 f.p.s. The spread was 21 f.p.s.

TSD 0.20-gram BBs on CO2

I weighed the Team Specialized Distribution (TSD) BBs and found them ranging from 0.19-grams to 0.20 grams. I think they are made from a plastic that’s a little lighter than the Sig BB plastic, or they may have more voids (air pockets) in them. Since these BBs are formulated by injection into a die they often have voids inside, though I will say that today’s airsoft BBs are much more uniform than they were 20 years ago.

The TSD BBs averaged 433 f.p.s. and ranged from 421 to 446 f.p.s. That’s a spread of 25 f.p.s. Again, the increase was anticipated because these BBs are just a little lighter.

0.25-gram Valkers Accelerator BBs on CO2

I have a wide range of airsoft BBs to choose from. They range from 0.12-grams to 0.30 grams. Because the M17 is so fast with 0.20-gram BBs on CO2, I tested it with Valkers Accelerator 0.25-gram BBs, to see how much it slowed down. This time the 10-shot average was 398 f.p.s. and the range went from 393 to 410 f.p.s. That’s a spread of 17 f.p.s.


While many think velocity is desirable — it isn’t with airsoft. With airsoft, it’s accuracy that matters. You don’t gain anything with more velocity because Hop Up keeps your BBs flying straight longer than gravity dictates they should. You just don’t want them curving to either side as they fly.

The M17 has adjustable Hop Up that I will discuss when we get to the accuracy test. My point here is that either 0.20 or 0.25-gram BBs may work in this pistol. We won’t know for sure until we test it for accuracy, which is no different than a pellet gun being tested with different pellets. In fact I have some 0.26-gram BBs I may test, as well. The CO2 magazine gives us a lot of options to explore.


Blowback (the metal slide coming all the way back to cock the hammer on every shot) does provide a small amount of recoil. It’s not as much as a .22 rimfire pistol, but there’s enough that you know you are shooing something. It’s certainly enough for realistic training. And the slide does remain open after the final shot.

Shot count

I expected to get a lot of shots on CO2, even with the blowback function. The M17 didn’t disappoint. The 0.25-gram BB (398 f.p.s. average) was still going out at 393 f.p.s. on shot 72. Then the gas ran out and by shot 78 the velocity was dropping fast. Shot 82 went out at 316 f.p.s. and shot 83 didn’t register, plus all the gas dumped.

Switch to green gas

To switch over to green gas, the green gas magazine was needed. This one has a port in the rear of the mag to accept bulk gas from a can. All green gas airguns operate by the injection of bulk gas from an outside source, and I have learned over the years that a new magazine probably needs a little time to break in. The first couple times you gas up, the mag may not take the gas well, or it may seem not to. But it soon settles down and fills easily after that. The M17 mag settled down on the second fill.

Sig M17 ProForce gas port
The port for green gas is on the back of the green gas magazine at the top, just below the valve face. The green gas cans all have a probe that fits over this spring-loaded port. Press the can in and allow the gas to flow into the magazine reservoir.

Green gas doesn’t fill as full as a 12-gram CO2 cartridge, so I expected fewer shots per fill. The number of shots per fill will increase a little as the mag breaks in, but it will never reach the shot count of a CO2 cartridge. Because I knew that, I filled the magazine before each 10-shot velocity test.

Sig 0.20-gram BBs on green gas

Sig 0.20-gram BBs averaged 339 f.p.s. for 10 shots on green gas. The low was 329 and the high was 354 f.p.s. so the spread was 25 f.p.s. That’s roughly the same spread as for CO2 (21 f.p.s.) and that tells me Sig has balanced this gun and both valves very well.

TSD 0.20-gram BBs on green gas

TSD BBs that weigh between 0.19-grams and 0.20-grams averaged 343 f.p.s. on green gas. The low was 332 and the high was 351 f.p.s so the spread was 19 f.p.s. Once again, that spread is close to what the gun did on CO2 (25 f.p.s.).

0.25-gram Valkers Accelerator BBs on green gas

On green gas the 0.25-gram BBs averaged 318 f.p.s. The low was 311 and the high was 321, so a spread of 10 f.p.s. which is again close to the 17 f.p.s spread on CO2.

Shot count on green gas

With green gas I got 22 shots per fill. The velocity started dropping after shot 5 with 0.25-gram BBs. After shot 20 it dropped very rapidly and I didn’t want to risk a stuck BB in the barrel. Over time I would expect the magazine to break in to get 25-30 shots per fill, so the best strategy with green gas is to gas up every time you load the mag.

Trigger pull

The single-stage airsoft M17 pistol trigger breaks cleanly at 5 lbs. 8.5 oz. (average over 10 shots). The single-stage P320 M17 firearm trigger breaks cleanly at 6 lbs. 11 oz. I can’t feel much difference between the two guns, and, while the numbers may sound high, when a pistol trigger breaks cleanly as these do, it feels much lighter. With many rifles the trigger pull is a big issue because of how you are holding the rifle, but when you are already holding a pistol in your hand squeezing a few extra pounds doesn’t make much of a difference — at least not with a gun you will fire rapidly.

Rapid fire

To get the shot count I fired the pistol as fast as my chronograph would calculate the numbers and noticed that on CO2 this pistol isn’t sensitive to cooling as it shoots. In fact many of the shots on CO2 in the high 60s since piercing the cartridge were over 400 f.p.s. with the 0.25-gram BBs. That was a pleasant surprise.

I didn’t see the same thing on green gas because the velocity began to drop after 3-5 shots. It continued to drop until the end of the magazine, and there was no recovery of velocity.

What that means is if you plan to train with the M17 or to use it for action pistol sports you should go with CO2. Go green gas if you plan to skirmish (war games where you shoot at other players), to keep the velocity down. In either case, buy extra magazines so you don’t have to fiddle with reloading while you are shooting.


That’s it for this report. If you have followed what I’ve said today you probably understand that the accuracy test will have to be at least 2 reports because, not only do I have two different gasses to test and a lot of different airsoft BBs to test, there is also the matter of adjusting the Hop Up. It should be interesting!

19 thoughts on “Sig Air M17 ProForce airsoft pistol: Part 2”

  1. B.B.,

    Obviously shot Count With CO2 IS an advantage but how does the Cost to Operate compare?
    How bulk can you go with the Propane refill source?
    I’m clueless on green gas.
    Will SIG ever go to a similar modular approach as they have with the actual P320…I’m thinking, for personal reasons, an X-Five training version. Does that look possible to you?


      • shootski,,

        I didn’t address your other questions.

        “How bulk can you go with the Propane refill source?”

        Most shooters just buy a small can at a discount store but with the right adaptors it is possible to use a big tank to fill. That would be the cheapest.

        “Will SIG ever go to a similar modular approach as they have with the actual P320…I’m thinking, for personal reasons, an X-Five training version. Does that look possible to you?”

        I don’t understand what you are asking there. This pistol would be the best way to train for the P320 M17 firearm. That’s why I am testing it.


  2. BB
    And that’s exactly what I wanted to know about the green gas compared to Co2.

    And that is a surprise that the pistol didn’t slow up rapid firing with the Co2. I like that.

      • BB
        I can see that they probably like that the propane is cheaper. But I don’t like that the propane slows up so much rapid firing.

        That’s actually why I like converting Co2 guns to HPA. You don’t get that rapid fire slow down.

        And that’s why I do like the pistol your testing on Co2. It didn’t slow down when rapid firing. If I got the pistol I would run it on Co2.

  3. B.B.

    When you say “Propane” is it the same stuff sole in 1 pound tanks used for blow-torches, Coleman stoves and lamps? Is the bulk propane the same 20 pound tanks as used for BBQ’s?


      • Hmmmm,

        No concerns that it is flammable?

        The bulk propane sold here stinks – literally – like hydrogen sulphide! Guess that with Co2 the gun goes PFFT and with green gas it goes PEW when fired LOL!!

        You would figure that some guy would add a piezoelectric igniter to the pistol for a “bit of extra power”.


        • Hank,

          Propane has no odor, so a scent is added to alert you to leaks. Green gas has a different scent added.

          Of course it is flammable. But the risk is low unless the shooters do stupid things that I’m not going to mention, because I know some of them can read.


          • Thanks for that B.B., I’m not at all familiar with airsoft products or green gas.

            Yes, lots of “stupid” going around – like the guy promoting deliberately diseling their springers! Lots of (uncontrolled and inconsistent) power and no brains!


  4. One of the things I liked about my Sig x-five bb gun before it broke, was that it had an adjustable rear sight.
    I see that combat style pistols don’t use them, but i found it helpfull. Nice replica, but not durable.My Luger needed its barrel fastened on better too, but it shoots to point of aim. Much more compact than the Sig too. I would pay more if they would up the quality. They just don’t hold up to regular use for me, but I like the realism.

  5. B.B.,
    That’s a great shot count with CO2; to quote Gunfun1, “If I got the pistol I would run it on Co2.”
    I like the realism of the pistol, and I’m really looking forward to your accuracy testing; I hope she shoots as good as she looks! Thank you.
    Take care & God bless,

  6. BB,

    Assuming that your figure of 115 psi vapor pressure for green gas wasn’t a misprint, how can you reduce the pressure 7 fold from that of CO2 and only get a less than a 1/4 reduction in velocity with the green gas. Is the tuning of the valve and hammer that radically different in the green gas guns?


      • B.B.,

        “…I called it a hat trick.”
        Okay Tom, let me try some speculation on how you get that relatively small drop in MV with the same hammer but a different valve/transfer port setup. The first thing to consider is the valve stem is being held closed by far lower pressure so the hammer will open the valve much quicker and hold it open a little longer resulting in more green gas volume to flow. To close the valve against a strong hammer spring takes either a stronger return Spring and/or a larger valve face because of the lower PSI of the green gas. The transfer port then needs to be optimized to meter the volume of gas to just equal the barrel volume.

        This is open not just to B.B. but to any and all of the readership for other methods speculation or corrections where you think I got it wrong.

        Close or no cigar?


  7. B.B.,

    Since you did not report the energy. As you may know airsoft energy is primarily given in Joules. Most airsoft ranges have chronographs and all players arms must be checked. They also carry portable chronographs so that players can be tested in the field by the officials.
    Some countries regulate it even further as to energy delivered. Same as airguns not able to go above a certain energy or velocity. Joules delivered does eliminate the affects of weight versus velocity.

    Silver Eagle

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