Sig Sauer MPX CO2 Air Rifle - Air side part 2

[@tmc4825]

The "Chatter" is the hammer not resetting on the sear. This is a "blow back" system. Its the same principle used in low quality paintball markers. They scavenge some air from the air that fires the projectile to also reset the hammer on the sear. Some areas to check are the point of interaction between the hammer and sear. Look for excessive wear where the sear touches the hammer. If worn, the hammer may slip off the sear several times before catching. These blow back operating systems are also sometimes dependent on back pressure. The pressure used to reset the hammer is higher when there is a pellet being fired. The force required to push the pellet causes the "back pressure" used to also push the hammer back to the sear. If therer is no pellet, there is no resistance on the air flow resulting in less pressure to reset the hammer. This causes the hammer to repeatedly strike the firing pin because its not bing reset, its free floating back and fourth. Also, Co2 losses air air pressure if fired repeatedly. The faster you release Co2 gass, the lower the pressure in the tank becomes untill it warms back up in a few moments. This loss of pressure can cause the hammer to not reset also. However, using HPA will alleviate that issue. Back in the hay day of paintball, I worked as a gun technician from 2000 to 2015. I've repaired 1000's of paintball markers and the functionality of this gun is no different. If your gun is firing more than once on its own, the hammer is striking the valve more than once because its not catching the sear. The cause could be one of a few issues. I dont believe its possible for the valve pin to "chatter" on its own. I hope this helps.

[@Shade112]

I've had my MCX sitting around for a year now due to a leak, and this video gave me the courage to open it up and get to the bottom of it! Thank you for both parts, good to have a no bullsh*t guide to follow. Saying that I couldn't find any obvious issue, just gave everything a clean and applied some Pellgunoil to the seals and it seems to be working great (only fired 1 magazine so fingers crossed). Edit for anyone wondering, the innards of the MCX appear to be near identical to the MPX.

[@johnclifford8140]

Thanks so much for your 2 videos. great help to me with trouble shooting my problem. Your camera placement was excellent. Your commentary was great as well.

[@torma99]

Thank you for your video and part 1 also. It helped me fix mine. The pin had fad fallen of, and the plastic spring thing was stuck in the same time.

[@brorjordas1979]

Yea. The firing pin falling out from the old MPX/MCXs is quite common.

[@brorjordas1979]

The firing pin popped outta my old MCX once. Once. I put instead an M4 cylindrical hex head steel screw into it and thru it. Took off the small knob from the rear of the hammer/bolt and attached a round 6mm thick nut to lock the new firing pin and to keep the main spring front centered in place behind the bolt. That all threadlocked and it ain't coming out again. The firing pin issue, along with a new "nipple" moving lug system was developed from the .22 Virtus PCP version and forward. I'd recommend you buy next the Sig Rattler Canebrake or the now outcoming MPX gen2. I definitely now want a gen2 MCX. My Virtus has been awesome - but I'd like a new MCX in .177 with the newest internals. That old thin co2 transfer line just does not work as well with air. My old MCX I had shooting way hard once - but the co2 cooled down so damn fast that it was not fun for that long.. I really woulda wanted the .22 Sig Virtus PCP in .177 also - just because the .177 ammo is cheaper to plink with.

[@williebeats4921]

I have the Canebreak Rattler version and it is holding up pretty well. Did have to tighten the barrel up a bit do to a slight wobble...but a simple fix. I'd advise anyone to use just a fine bit of loctite when performing this on the barrel, on all four screws. I'm running on an HPA system and are seeing high 600's in fps using 7.9 grain pellets and low 600's using 10.5 grain...in which brings this rifle to an 8.2 ft. lbs gun from the muzzle. Note that I have customized my regulator to consistently output 1800psi using 10 stainless steel Bellville washers and two 0.02 thickness shims to achieve a consistent output. While your standard 3000psi 13ci tank outputs an 800 burst, it with perform at its optimum around 2200-2500 on the input side. I will be purchasing a MPX G2 to find out what's going on with the internals. If they have changed, I'm definitely rebuilding my MCX with better parts. Longer barrel means higher FPS. Good luck Airgunners

[@brorjordas1979]

@@williebeats4921 I've been having an approx 1450psi outputbon my Virtus and it has done quite well. But apparently many has liked that 1800psi mark..I think I oughta try getting that output the next time I drain my airtank and see the fps numbers.. Thanks for the good comment!👍🏻

[@chancedickerson8877]

Thanks so much for the video. I had taken mine apart and some of the pieces fell out and didn't know how they went in there. You are right about the gun. It is a nice looking and had potential to be a great pellet gun but very poor as soon as you open it up. I am tired of going thru 10$ cylinders for only about 5 shots . I got an adapter that I havnt tried yet because I didn't know how to put the thing back together but do now thanks to you.

[@TedSchwabenbauer-h9g]

This MPX is configured the same as my MCX but my issue is a bit different. With about 300-400 rounds through the MCX v.1 CO2 air gun, it out of nowhere, stopped firing. Unlike this and other similar reviews I have read, mine is not an issue with pressure leaks or the hammer popping out of the bolt. It took a long while to determine but it appears that the hammer, when pressed in at the factory, is pressed to a very specific depth (from the front of the bolt). Thus, the hammer had not been seated against the bolt, leaving an additional amount of space before the hammer would actually seat against the bolt. My suspicion was that during the initial 300-400 rounds, the impact of the hammer against the firing pin, finally pushed the hammer deeper into the bolt. Now, having increased the distance between the hammer and the firing pin, it prevented the bolt/hammer mechanism from actually contacting the firing pin. I popped the hammer out of the bolt and added a washer of 1.4mm thickness to the shaft of the hammer then reinstalled it back into the bolt. The MCX is now back to firing. Extremely poor engineering. Shame on you Sig.

[@Outdoorshuntingshooting]

The internal metal looks like some kind of zamec type alloy, really weak, shame, if they used 7075 aluminium alloy with better seals, gun in theory would be much more reliable and last much longer.

[@kirmu409]

How can i press off the nylon washer from the rear of the valve? I didnt know it was pressed with the metal piece and i took only the nylon washer away. Now i have four new nylon washers/seals that i want to test if i get the gun back in bussiness but i dont know hot i can add the nylon washer in without taking off the centerpiece EDIT: Seems like it was very loose and i got it off just by pulling

[@jantelow]

There is something strange about the way of thinking with Sig and their experiments with mcx and mpx that give bad results. I guess it has something to do with the production costs. After 5 years they have finally solved the problem with the firing pin on the mcx and mpx by serrating it, but they have replaced the brass sleeve that holds the nylon gasket in place at the back of the valve body with a sleeve made of the same crap material as the rest of the innards, so now it is this sleeve which falls out instead. This brass sleeve on the older versions was as tight as if screwed in. The older versions also had a better construction of the air supply with screw connections at the brass tube that pressed against the o'rings. It would have been better if another airgun manufacturer that takes pride in making good airguns had taken over the production rights and made the necessary improvements, then these airguns could have been really good.

[@Aleks-Milenkovic]

My mind keeps going to the idea that maybe replacing some parts with a more robust metal but say im right and we replace aluminium mechanical parts with steel parts how will that affect the momentum and timing of the function

[@18tegan]

Great video, very very helpful, I just wished I discovered it sooner 😅

[@LivingEpistles444]

I'm wanting to paint my mpx to a coyote brown. I figured I would take it apart and paint what I wanted with some rustoleum. While I had it opened I was gonna clean and oil some parts. Should I just use pellgun oil? Is there any pitfalls I need to be aware of before opening it?

[@pabroon74]

The only think that might fly off, is the safety switch. All of the mechanism is attached to one side of the inside of the casing - except the safety switch, which is attached to the other side. Pellgun oil - I think - is meant or rubber O rings. It's probably worth treating those to promote longevity. I didn't bother oiling anything else, it's all so clunky it didn't seem like it would make a difference. But I could be wrong.

[@LivingEpistles444]

@@pabroon74 thanks for the quick response!

[@stanlyipkiss8303]

Mines leaking from the big white o ring where the pin punctures the co2.. it sprays out right by the slide hammer

[@pabroon74]

I did replace that big white O ring on mine as a matter of course. The advice I got was that the O ring material was too hard - it needed to be more 'rubbery' so it would seal properly. I tried other neoprene options, but ended up putting a new nylon O ring in. Then I took a wee bit of material off the back of the floating pin thingy so more air would escape to cock the mechanism.

[@stanlyipkiss8303]

@@pabroon74 do you remember where you got the replacement o ring I can't find one anywhere but the UK and they don't ship to the USA...

[@pabroon74]

@@stanlyipkiss8303 You can buy seal kits from eBay. Search there (or on Google) for MPX seal kits,

[@stanlyipkiss8303]

@@pabroon74 I've tryed can't find that big white one or anything similar only on one website but it's in the UK and won't ship..

[@pabroon74]

Ah... It might be a standard size nylon washer. Measure it and find a seal supplier online. I actually didn't mess with that part of the gun, (I thought you meant another wee nylon washer in the blowback mechanism.) I have PCP air guns, so have a compressor. If the gun operates well, it's worth an HPA conversion.

[@PNWLiving1725]

hopefully it is fixed

[@tonyhowell5283]

my black shroud has disintegrated suffice to say I am getting loads of air from the magazine and about 1fpe!! any ideas where I can get one?

[@pabroon74]

Afraid not. The only spares I could find were washers and seals. Sig aren't doing any service parts. You could maybe cast about for another gun someone might be off-loading due to other faults? You'd need to be lucky/quick though. Surprised the shroud gave up, it seems fairly sturdy. Mind you, with this gun - who knows. 😕

[@tonyhowell5283]

@@pabroon74 got the mcx valve kit from Bagnalls - looks a bit different but will try and fit it this week

[@GGaievski]

is there any way i can make it full auto?

[@pabroon74]

I wondered about that, but no. Mechanically, this gun was never designed to work like that - even in the US market, it was a semi-automatic action. Shooting pellets, I don't think would ever work on full auto. It would need to be BB.

[@musayaka9956]

hi! Can I turn this gun into a fully automatic PCP? My fingers hurt and I'm tired.

[@pabroon74]

Heh! No. The belt holding the pellets only cycles when you pull the trigger. There's no way to make this gun fully automatic. Being as I am in the UK, I've also got to say, attempts to do so would be exceedingly against the law. :-)

[@derekwngreen]

It’s a semi automatic weapon so it won’t reset the hammer! That is moved back with the operation of the trigger each pull of the trigger pulls back the hammer till it’s fully depressed then it is released forward..!

[@pabroon74]

Not sure what your point is. The action of the trigger releases the pin carrier (held back on the main spring via the trigger sear) - which strikes the floating valve - which allows high pressure air to drive the pellet forward and the pin carrier backward thus recocking the gun. The gun needs to be manually cocked before operation. The blowback action recocks the gun, not the trigger pull. The trigger pull just releases the pin carrier. Or maybe that's what you meant?(!)

[@derekwngreen]

No blowback on this gun it’s the trigger that makes the hammer move back on the big spring!

[@pabroon74]

​@@derekwngreen Nope. The trigger does two things; actions the sear that releases the 'bolt carrier', (in this gun, it's a pin that taps a floating valve), and advances the belt in the magazine. That's why you have to cock the gun with the charging handle on first use. Gas pressure recocks it there-after.

[@davidglenn2739]

Be careful not to turn on the air while apart! I just about lost an eye! lol

[@chrisvalenzuela3516]

I put mine back together n the trigger won't pull why is that?

[@pabroon74]

Howk it apart and check the trigger seer is seated correctly - and the bar & spring that gives the safety catch it's snap is in the right place. (The safety catch bar & spring is the only thing attached to the case on it's side. I can't remember if it's the left or right.)

[@Akmt96]

I just did all this and the thing just spit out a whole new 88g canister. It started with a bit of a sputtering of co2 after a couple shots and a slow leak, after taking it apart and putting it together it just spit it all out without stopping flow. This thing was such a waste of money

[@pabroon74]

Yup. It is incredibly frustrating, because it's a good looking thing, and should be so much better.

[@FallenPhantom0]

Great video very helpful thank you

[@jgbelmont]

Pot metal and dreams hold these together. I am surprised they shoot at all.

[@pabroon74]

Sad to say, but true. They look great, but much like the materials, it's pot luck if you get one that works. And to fix... You need to be prepared to get in about it - and, also be prepared to bin it.

[@jgbelmont]

@@pabroon74 From a company like sig they could make a really really nice product. But they didint. Like 900 fps semi auto would be cool. But quality.