The Real and Dirty on the Tokyo Marui M870 Shotgun ( hpa tm m870)

[258eagle]

Many searches came up empty so I thought I would share my experience so that others may have the information i could not find. This posting will cover the two major flaws of the tm870; gas and leaks(really only one reoccuring leak).

 

I hope I help my fellow shotgunners!

 

So quick review-

 

-Gas shotgun has a true range of 150 ft on 3 shot!

-TM quality

-Takes those cheap spring tri shot shells

-Tank gets me about 7-8 shells worth (way less on 6 shot mode and only 50 ft range)

 

Nothing new here that you cannot find elsewhere, I want to get to what it is like to own one!

 

The real deal;

When this shotgun does work it is truly impressive, the first skirmishable airsoft shotgun i have used and it meets field requirements of 1 bb firing below field limit fps (not many other gas shotguns can do this). The Range is shorter than an aeg but not by much! Nothing using cover can't fix. In milsim ops use I never felt out gunned. But there are caveats to this airsoft shotgun, large issues that I cannot believe other reviews have not touched upon.

 

Propane is too much(psi is too high) for this shotgun, green gas(again psi is too high) is too much for this shotgun, 6 shot is worthless, no confidence in the gas tank, and the shotgun leaks often. Constant disassembly and regreasing are required.

 

It did not last the entire game at OLCMSS Freelander

 

 

 So what makes this shotgun worth owning if in stock form it doesn't even work? POTENTIAL

If one can get a reliable power source and stop the leaking, this individual would be left with a truly skirmishable shotgun that is no longer a novelty item but a force on the field!

 

So i attempted this because a great airsoft shotgun is something i always wanted.

 

Here is how I achieved this;

HPA!

and it was incredibly easy to do.

There are a few routes to go; $200 angry gun m4 stock with a hpa fill nozzle replacement(ugly and expensive$$$ route!), drill and tap the gas tank, or mod your current gun to hpa for $20.

 

Here is how I hpa'd my tm870 maintaining the original stock and maintaining the potential to return to factory gas set up.

 

Step 1-    Split the original stock in half (be carefull of glue, use acetone or heat)

 

Step 2-   Cut out old 8mm tubing and replace with a desired length 8mm tube(easy to find 8mm plastic tubing online, i got mine from amazon)

Step 3- Get a 8mm 1/8" threaded hose fitting

Step 4- Get a 1/8" threaded male quick disconnect (i got mine from amped airsoft)

Step 5- Drill 8mm hole in the bottom of the stock grip.

 

What these steps look like:

 

Final steps- reassemble stock (glue if necessary)

 

BAM! HPA shotgun for about $20 in parts.

 

Why hpa? if you live an area with more than one season then the gas tank will not be reliable or usable all year long, or are tired of playing and having the fear of running out of gas.

 

Next Issue: LEAKS! So many leaks!

This shotgun leaks so bad i can't believe it isn't talked about more. My only leak always came from the output release valve inside the "gearbox" shell of the shotgun.

 

So i did the typical move and bought the cure-all SAT output valve!

 

Well it didn't work at all (this was prior to hpa)! After so many positive reviews this new valve lasted longer than original but only about 3 days of play. I thought this was me using propane so i took everything apart and greased everything. I only used green gas after this and still leaks! SO disassembly and grease again... Next came hpa at 80 psi, the shotgun performed terrible at this low psi and after 3 games leaks! it emptied my air tank. No way was I going to rebuild and grease this shotgun every week so i took it upon myself to come up with a solution.

 

The Leak Fix;

 

I was never happy with how the valve, the portion that was struck by the hammer, returned to the ready position. It did not seem very firm. The valve failing to return to close was causing the leak. I decided to put a stronger spring in the output valve. I took 4 coils off the factory tm output valve spring and installed it into the SAT output valve. the Valve returns very firm now. I was afraid this meant I would need a better hammer spring and go on a trial and error phase but nope! it worked and worked like a dream. I am 500 shots/slamfires in and 100% performance. I am going to op red storm east soon and will report back.

 

What would have I done differently?

 

Never gave $80 of my dollars for the SAT output valve, instead go out to a local hardware store and get a stronger spring for your factory tm output valve and i believe you will be just fine.

 

Other:

I have heard other users had issues with the nozzle and a loading arm, both plastic which can break, metal aftermarket parts are available. At this point my parts show no wear so I did not cover that area. These two parts, gas, and leaks are about the only problems I am aware of with the tokyo marui m870 gas shotgun.

 

What is it like now?

Epic, I am running 95 psi, getting 150 ft with .28g bbs, and 330 fps w/.20g bbs. It was very effective to use and great fun! No longer fearing of running out of gas means i shot a lot! and it didn't leak a bit. I shot 40 shells today and had a ball. Prior to hpa i never would have fired so freely.

 

 

[Wingmann]

Nice! I still prefer the Angry Gun stock for ergonomic reasons, but your mod makes all the sense.

[renegadecow]

FYI you can also stretch and retemper the stock spring to increase tension. The one I did to 130% original length holds gas but sometimes still leaks. Then again temperatures here puts green gas over 130psi. With the o-ring spacered hammer spring clocks 336fps with .25g which is about 370 on .20g. Currently baking a spring stretched to 150% length to see if it fares any better. More than that and I'll need to switch to an AEG M90 spring.

[renegadecow]

And a 150% stretched spring still leaks. Well, sort of. Just like the previously tested 130% it holds gas fine enough on its own, but after a dozen or so rapid fire shots begins to leak. Then if I leave it alone to warm back up it goes back to normal. At this point I'm inclined to believe the o-ring on the valve is getting frozen or at least made hard enough with the drop in temperature to cause an imperfect seal. The stock o-ring is already surprisingly very hard, about D90 at a guess which is unusual for TM. I have D70 o-ring here that I have yet to try and will chime in the results shortly.

 

edit: No good. D70 o-ring of the same dimensions (2x4mm) just gets blown open by the gas pressure. I'm out of ideas other than making a PEGASUS valve for it.

[258eagle]

You can find springs of the same size at different rates at some hardware or hobby stores. Also cutting a coil or two will increase the spring rate. I am not using gas so i do not have the cool down effect but my chopped spring has been doing wonders so far.

[renegadecow]

If I weren't on the bloody equator I swear this damn shotgun should be working perfectly right now.

[scorch]

Seems to me that with a check valve and a Y-piece you could have it running on either HPA or the internal tank, swappable at a moment's notice.

[258eagle]

Scorch you're not wrong, i got the parts on saturday and was playing sunday. Lol

i also don't plan to return to gas because of the unreliability, i mainly did this because of potential resell and i hate tapping the tank.

[258eagle]

Renegadecow i feel ya! Live in america on the east coast and we have 2 seasons, blazing summer or blizzard cold. I suggest going hpa and keep at it! I am about 15 rebuilds in and the shotgun works now. i totally say it was worth the headache.

[renegadecow]

That's just it. The two I'm fixing aren't even mine! My personal scattergun is a Serbu made from a china clone Mossberg and runs like a champ despite having the similar reversed valve design as TM's. Though as I recall it's got a massive spring holding up against the back pressure. From my calculations, to make the TM work here I'd need to fabricate a spring that holds up at least 31lbs to stay closed.

[Alias1983]

My m870 took gg and did not leak, But it did not feed.

 

3 shot mode I got 1 bb, 6 shot mode I got anywhere from 1-5 bbs.

 

I attempted to fix it, did not work so I sold it.

 

It was my first tm and I was expecting awesomeness, I even used duster gas to start with even though I was told it could handle the gg.

 

I was getting 1 bb in 3shot, 3 bbs in 6 shot. Ran out of duster and tried gg.

 

That's how I got it to actually somewhat feed right in 3 shot mode.

 

So the transfer bar was bad or so I was told.

 

Never fed on clone shells, 99% of the time the clone shells were trash, I lost money on this deal.

 

I really wanted it to work, but its just the Airsoft "bobs" telling me to get a aps 870.

[Pascotam]

I have installed Angry Gun's (gas tank) stock to it.

 

 

~ Pascotams iPhone TapaTalk

[258eagle]

Update:

 

I am +10,000 rounds through the shotgun running at 115 psi and I report ZERO issues. I continued this project assuming I would need to spray oil in every few hundred rounds, do a tear down & grease internals every 5,000 rounds but nope! I have converted the shotgun to hpa and put in a stronger valve return spring and the gun is performing as it should. I have used this shotgun with great success at Lion Claws Operation Red Storm East and solely use this shotgun in my weekly skirmishes. 

 

 

I continue to improve using this gun, there are some difficulties using a manual operated shotgun vs polar stars but it is a blast.

 

I have found that Six Shot mode is not entirely useless, in fact in very close quarters battle it is down right dirty, lol. 

 

Six shot is devastating in cqb but once you exceed cqb at any level it is back to being useless.

 

More Upgrades;

 

I have been harassed since day 1 about cutting the outer barrel down, selling to get a breacher, get an m4 stock; blah blah blah.

There is some truth in what they say, the inner barrels on the full length tm870 are the same length as the breacher version(260mm). 

Lastly I was impressed with the performance but knew that just a tad better would send this shotgun over the top.

 

I present to you the Wii Tech M870 Long Inner Barrels Set (6.03x380mm)

 

               First outing didn't go well, I saw no increase in performance. I then switch from .28g or green .25g bbs to white .25g bbs and that was key. The fixed hop up doesn't handle .28g bbs well; and my green bbs were not visible. When i switched to .25g white bbs and saw the distance I was amazed. The improvement showed on my next skirmish as I could engage all those who engaged me. No longer did I have to wait for enemies to come in range. The grouping is better but not too noticeable as the grouping was always good.

               Favorite part of this barrel set is the spacers/holders included with the barrels. A little more difficult to install but the spacers are so solid and eliminates that annoying nut strip on the ammo tube ring. After installation there is zero barrel wobble and it is by far one of my favorite aspects of this upgrade.

 

-Secondly I got the wii tech rail handguard

 

It is an exact clone of a troy trx but changed to fit a shotgun. I love that this replaces the old set up. I can now easily re tighten the arms without disassembly, the arms often come loose. The rail can be removed without any diassembly and reveals screws to allow a lot of gun disassembly without dissembling the barrel assembly(a good amount of time saved here). the bottom rail does not remove like a real trx so in the future i will be getting a trx and cutting it to fit for an even slimmer handguard. the rail hooks onto the pumps arms like any rail attachment for a trx, spacers through the trx squid holes and screws into the arms. Very simple and thought-out. 

 

Wii Tech is a hong kong airsoft company that CNC's their own stuff. Never heard of them before but their products have been of superb quality and I love them.

 

 

 

[renegadecow]

What sort of fps bump did you get with the barrels? The only other ones available are by SAT and are the same length as stock. And it would have been convenient if they just incorporated the nut for the magazine tube ring into that chunk of metal holding the extended barrels.

[258eagle]

What sort of fps bump did you get with the barrels? The only other ones available are by SAT and are the same length as stock. And it would have been convenient if they just incorporated the nut for the magazine tube ring into that chunk of metal holding the extended barrels.

Not much really but it sure shoots better!, not a better grouping but instead holds the grouping a longer distance. the SAT ones are 6.01mm.... asking for jams with that. and it is super convenient because they did!