Tokyo Marui M870 Tactical Gas Tri-shot Shotgun- picture, text and video review

[Baddbaz]

The older inefficient tm guns hold up better than the newer more gas efficient designs , glocks eat slides on propane , 57 shears its lugs , mp7 its the nozzle , only the px4 and m9 seem to hold up out of the newer models , even the xdm cracks its slide on propane . Have seen quite a few recently .

[PureSilver]

I'm not sure you can compare a general pattern gas cannister with design specification to comply with international transportation law and usage with the issue at hand, especially when you are comparing this to a gas tank that was designed for essentially a recreational replicate toy gun. [...] I have to wonder if it's due to factory production side or a deliberate in house decision, i.e. cost cutting, change of management, etc etc.

 

Ordinarily I'd agree that you shouldn't compare such things, but consider a 'green gas' can for a moment. It's nothing but a container for the actual product (silicone and propane), costs fractions of a pence to make and is about a quarter of the thickness of the M870's magazine at most - and yet it could easily withstand these pressures and probably exceed 150% of them quite safely. If a $0.05 deodorant can is tougher than a $34 magazine, clearly there's been failures at several levels of TM.

 

I want to emphasise too that this isn't just a 'you shouldn't have used propane' problem; these magazines ought to be capable of handling at least 45-55 degree weather with 134A, and yet clearly they can't. I'd say this is either a catastrophic failure of metallurgical QC, or it's a design failure that's been allowed to propagate all the way through to production. Neither of those possibilities inspires much confidence, to be honest.

 

I know we're not just talking about the M870 but it, being NBB, shouldn't need any upgrades for propane (the exploding tanks notwithstanding). And the TM 1911, Hi-capa, 226, M9, Deagle and plenty of others are very accommodating of propane completely stock. No metal slide required (they just reduce performance).

 

That, IMO, is especially frustrating - the rest of the gun appears absolutely capable of taking the increased pressure of propane without issue, just like you'd expect a NBB to be able to. That the magazines, of all things, should be the weak point is just stupid when TM's been making guns since the early 1990s whose magazines could take propane without issue.

Edited September 27, 2013 by PureSilver

[onizuka-gto]

 

Ordinarily I'd agree that you shouldn't compare such things, but consider a 'green gas' can for a moment. It's nothing but a container for the actual product (silicone and propane), costs fractions of a pence to make and is about a quarter of the thickness of the M870's magazine at most - and yet it could easily withstand these pressures and probably exceed 150% of them quite safely. If a $0.05 deodorant can is tougher than a $34 magazine, clearly there's been failures at several levels of TM.

 

I want to emphasise too that this isn't just a 'you shouldn't have used propane' problem; these magazines ought to be capable of handling at least 45-55 degree weather with 134A, and yet clearly they can't. I'd say this is either a catastrophic failure of metallurgical QC, or it's a design failure that's been allowed to propagate all the way through to production. Neither of those possibilities inspires much confidence, to be honest.

 

 

That, IMO, is especially frustrating - the rest of the gun appears absolutely capable of taking the increased pressure of propane without issue, just like you'd expect a NBB to be able to. That the magazines, of all things, should be the weak point is just stupid when TM's been making guns since the early 1990s whose magazines could take propane without issue.

 

 

Gas cannister are a circular shape for a reason, it can have thinner walls because it's stronger structurally.

The TM tank on the other hand is a elongated oblong, naturally it'll be weaker than a circular shape, but on the other it is equally very easy to rectify reinforce with simply thicker walls. You only have to see a Maruzen pistol grip tank, a short oblong shape, but the thickness of the metal is clearly as tough as what you would find on a TM glock magazine.

 

I don't think the problem is entirely a metallurgical issue, after inspecting it closely i see some merit in Baddbaz comment. If i can replace the end pins with a flat head bolt that gives enough clearance to be slotted back in or even a rivet, it might prevent further deformation that'll lead to permanent damage.

 

However i suspect that the minute i knock those pins out the casing, it will pull the holes out of alignment/backplate popping off, etc.

 

Those pins were put there to resist movements on a horizontal and vertical planes. They were definitely not design to resist lateral movements i.e. expansion to the sides or they would not just be pins but bolts with fasteners.

[Baddbaz]

Was thinking along the lines of the blind screw pin where the pins meet halfway from either side and screw together in the middle . , not sure of their technical name . But they usually have a dome cap or flat screw end . In the middle they screw together to make one pin . Don't think they make them small enough though . The other option would be to solder / braze son material onto their ends ( possibly a small washer ) to stop them pulling through the tank casing

Edited September 27, 2013 by Baddbaz

[CatgutViolin]

If these parts are deforming under the pressure of propane, then shame on Marui for such poor engineering. The standard rule is that a gas container should be able to withstand three times the pressure it's rated for. If the tank is meant to be used with HFC-134A, which is a little over 80PSI at typical room temperature, then it should be able to go up to 240 PSI- and that's double what propane is under typical UK/US use conditions.

 

Deformative expansion over time can lead to structural failure and possibly kaboom. For a part to risk this at just over its specified operating pressure is extremely unimpressive.

Edited September 27, 2013 by CatgutViolin

[Stuey]

If these parts are deforming under the pressure of propane, then shame on Marui for such poor engineering. The standard rule is that a gas container should be able to withstand three times the pressure it's rated for. If the tank is meant to be used with HFC-134A, which is a little over 80PSI at typical room temperature, then it should be able to go up to 240 PSI- and that's double what propane is under typical UK/US use conditions.

 

Deformative expansion over time can lead to structural failure and possibly kaboom. For a part to risk this at just over its specified operating pressure is extremely unimpressive.

 

Thank you, this is what I was talking about with regard to safety margins. Very sloppy unsafe design.

 

We can only hope Marui improve the design, or an aftermarket company jumps in to fill the gap.

 

Shame, as the rest of the gun (bar the hop thing) seems really solid.

Edited September 27, 2013 by Stuey

[PureSilver]

The standard rule is that a gas container should be able to withstand three times the pressure it's rated for. [...] For a part to [deform] at just over its specified operating pressure is extremely unimpressive.

 

This is exactly what I've been trying to say. That these tanks should be going all Marlon Brando on us at such low pressures (<130psi maximum) strikes me as a manufacturing failure, because I just can't see how anyone semi-competent could allow them to be designed to fail under these minor stresses. The rest of the gun appears solidly designed and engineered, and the only other problem (the hop-up) has been traced to assembly, rather than design. Why would you put so much work and expertise into the gun, and then make the magazines out of papier mâché? It doesn't make any sense.

[bankz5152]

Kinda gald i didnt get one right away...

 

 

Sent from my GT-I9300 using Tapatalk 2

 

 

[Aod]

Other than the fear of the possibility of catastrophic failure, have any gas magazines actually failed?

I have two gas-magazines for my M870, the one that came with the gun and a spare. The spare came direct from Japan, still sealed from Marui, still containing gas. Before using either magazine, I did notice that the spare was "bulged" compared to the one that came with the gun (received empty).

 

Both gas-magazines have had green in them since receiving them, and they've both been sitting, filled, on my shelf for about three weeks now. The Mag that came with the gun has bulged a little, the spare hasn't bulged any further.

 

Given the geometric design of the magazine, a small amount of deformation can be expected, and given that there have been no known incidents of failure, I doubt it's likely to be an issue.

Furthermore, even if the magazine walls bulge to the extent that the middle pin escapes both walls, the other two pins, being much closer to the rigid edges will still hold the baseplate in place, allowing all the gas to harmlessly vent out the gaps. There will be no "face shattering explosion".

 

Lastly, If it becomes that much of a concern, there is no reason why you couldn't pop the middle pin out (while the magazine is ungassed ¬_¬) and replace it with what looks like an M3 bolt and securing nut, there is sufficient clearance within the stock for this.

Edited September 28, 2013 by Aod

[renegadecow]

Gotta say my Tanakas have taken Green Gas just fine

Yeah, gotta say they hold gas pretty well. Marushins too in most cases. While the Japanese are limited to using 134a, their guns are not always necessarily limited to it. On Marushin manuals for example they only say to "use the right (airsoft) gas" without mention of 134a only since they do export their guns and are probably well aware of people stuffing green gas in them. Most cases where green gas fails on a Japanese gun is down to seals which are easily remedied. On this 870 however, it's more of design limitation. The gasses contained in gas guns are measured in PSI and with the larger surface area of the 870 gas tanks it's technically holding more stress than the usual pistol mag. It needs internal structural reinforcements as you would likely see in AR magazines. For a clear example of some really bad engineering, one only needs to recall the first generation WE M4 magazines.

 

Even Redwolf Airsoft states on their website that it runs on green gas.

They also incorrectly list hop up (between none, fixed and adjustable) and a single action army as "semi automatic" among other things. For all I'd care they can say it runs on gasoline.

Edited September 28, 2013 by renegadecow

[Wingmann]

Is it really. Cheaper in the long run when you take into account upgrades required ( metal slides etc ) and the reduced lifespan of the gun and accelerated wear on parts , not to mention the loss of warranty repairs ?

It is, as I don't own any plastic made pistol. I mainly use KJWs and KSCs of several sorts, most of them CO2 ready.

[lacanuck24]

This would be the perfect justification for a buffer-tube style collapsible stock with a cylindrical gas tank!!! But a bummer for needing to use the oddly shaped tank for the full stock. Where can we get some of that magic metal Wolverine is made from, that ought to hold up.

 

I was in paintball for a number of years and have seen burst disks, carbon fiber compressed air tanks, and steel braid hoses all blow up. The fact that these tanks aren't holding up well to even a bit of over pressure or heat is way more than disconcerting. Plus the girlfriend will never let me live it down if the tank explodes and totally ruins my security deposit. 

[mellvis]

So just to reiterate, using a sling on the m870 is NOT recommended? I just got mine today and was thinking about how sturdy it is.

[Crashcat]

Found this on a fb group I belong to. It's from a shop here in HK.

 

[gsquared]

Ok took mine out today ..ambient temp about 78 degrees

 

1)Horrible gas effiency ..I'm gonna say not even two shells before it's done

2) jams jams jams...theirs shells kept jamming when pumping new shells not so much

3) when gas is new awesome range ..it poops out as you expel gas..refer to item 1...

So in the end a few shots and it becomes useless in battle

 

 

Something's up. :-((

[sacairsoftsn00py]

You might have damaged your nozzles as well.

 

Aside from shooting 5 bbs instead of 6. Mine has been flawless with 152a and 134a gas. Excellent gas efficiency.

 

Sent from my Samsung Galaxy S4 using Tapatalk 2

 

 

[mellvis]

Im also experiencing the 5-shot problem on mine. From a certain point of view, its actually quite nice since i get an "extra" shot per shell. But i am concerned about its long-term effects (if any). Still a fun piece of kit nonetheless!

[Wingmann]

1)Horrible gas effiency ..I'm gonna say not even two shells before it's done

Are you filling her up properly? My Madbull adapter and other bottles don't fit that well on the filling valve and I have to insist quite a lot until I get a decent fill.

[Baddbaz]

Its a case of listening to the gas going into the tank , once full you can hear the gas stop filling .if you try to fill it up like a mag it vents gas like its full when it is not .

[blobface]

Its a case of listening to the gas going into the tank

 

Not sure I want to put my ear that close to the tank after reading this thread..  

[Baddbaz]

Who said that the 870 didn't have blowback .. Lol

[Inari]

Pfft, this is Marui...it's the new innovative blow-up. It uses up one whole gas tank at a go, but the shock and awe it inspires is worth the decrease in efficiency

[DrAlexanderTobacco]

Considering the tank's in the stock, this clearly means Marui designed the M870 as an airborne weapons platform. Slap the stock and fire the entire shotgun at the enemy.

[sacairsoftsn00py]

How many mags have blown up again?

 

Exactly...

 

Use it per manufacturer specification...if you have problems then...contact the retailer you bought the gun from.

 

Having issues cause you used a higher pressure gas? Who put green gas/propane in it ..you. who's to blame? Marui. Lol

 

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[blobface]

http://en.wikipedia.org/wiki/Joke