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6mm Acm M500 Constant Air Rig


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25 replies to this topic

#1 filipinofreak

filipinofreak

Posted 01 November 2008 - 06:21 PM

Quick Review:

I'm new to airsoft shotguns. When I was looking for a skirmishable shotgun to use as a primary weapon, I came to the conclusion that the best options were the 6mm ACM M500 or a tri-shot springer (TM, UTG, TSD etc.) I settled on the M500 because I loved the feel, look, lack of shells and 5bb spread. However, I was a little disappointed after fielding it for the first time. The gun shot very consistent with good range and a nice spread, but only for the first 5-8 shots. The gun holds enough ammo for 24 full shots, but will only do ~16 shots with usable range. I wanted to use this gun as a primary, and having to carry gas around and refilling under fire would not do. Not mention the the problem of finding parts, especially fill valves. So I jumped in and decided to go for broke. I was either going to modify the gun to meet its potential or completely destroy it in the process.

Air Rig Modification:

The most irritating feature of the gun is its inadequate gas reservoir. The gun performs well at higher pressure and only the first several shots get to take advantage of that. I had my CO2 tanks for paintball around, so I decided to build an air rig and adpt the M500 to constant air.

Here is the fill valve:


The valve screws into a metal nub the sticks out of the bottom of the gas reservoir. I had two options to adapt the gun to take air fittings: fill valve external CO2 adapter or drill/tap the gun directly for common 1/8 npt fittings.

KWC style fill valve CO2 adapter:


I chose to drill and tap for 1/8 fittings. I didn't like the idea of the adapter because it is difficult/expensive to get parts that are compatible with the quick connect adapters. Also, no one could tell me with any certainty that the adapter would fit. Here is the finished rig (no pressure gauge installed in the pic):



I was planning to do a step-by-step build report, but I was on a roll last night and neglected to take photos while working. Maybe if I convert an 8mm version, I'll do a build report. Feel free to ask questions if you're thinking of doing the mod though. We need more shotgun players a-yesnod.gif

I used a paintball remote hose to get the hose and quick connect fittings for this project. It is a quick/cheap way to get the parts needed, but they put some sort of adhesive sealant on the threads that take A LOT of force to unscrew. I damaged the on/off valve and ASA adapter on the ends getting the hose and fittings off.

Paintball remote hose:


Here is the fitting into the bottom of the gun:




I looked up the vapor pressure of propane. It reaches ~200psi when it is at 90F. This is the max I'll run the gun at. Currently I'm running 150 psi into the gun and It's firing better than a full fill of gas. The modification is working fine for now, but still need to test it out in a game. I don't think I'll have any problems with the system though, it's straightforward and simple. I am now the proud owner of the coolest shotgun ever a-rolleyes.gif Not really, but it's perfect for me a-thumbsup.gif

Next project might be an 8mm version or add a tightbore to the current gun. I also want to shorten the external barrel.

Conlusion:

The ACM M500 is a beast. It's heavy, intimidating and has power that few airsoft shotguns can match (400+ fps with one bb). Unfortunately, it is underpowered and finicky in its stock form. If you want a super reliable shotgun with good performance, get a tri-shot springer. If you are willing to put in time and money (not a lot of $$$ compared to AEGs), the ACM M500 will be one of the coolest airsoft guns you'll ever own.

Edited by filipinofreak, 01 November 2008 - 07:49 PM.

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#2 Fatboy 589

Fatboy 589
  • Gender:Male
  • Interests:Skateboarding, Jesus, airsoft, real steel guns.
  • SOA Name: Fatboy 589

Posted 01 November 2008 - 07:28 PM

Sweet review, love the idea you had with hooking up the gas tank to it.
I wanted an ACM pistol grip shotty, but the gas is so annoying, so I've just kept my UTG M3. But kudos to you, bud. Really good job with that!

Edited by Fatboy 589, 01 November 2008 - 07:28 PM.

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ohai

#3 Hush02

Hush02
  • Gender:Male
  • Location:Hawaii
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Posted 01 November 2008 - 09:51 PM

Looks deadly man... you got an fps estimate on that?
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#4 filipinofreak

filipinofreak

Posted 02 November 2008 - 05:06 PM

QUOTE (Hush02 @ Nov 1 2008, 04:51 PM) <{POST_SNAPBACK}>
Looks deadly man... you got an fps estimate on that?


Haven't had a chance to chrono it yet. I did some coke can "chrono" tests with one bb in the chamber. It pierces the bottom edge at 1". That is about 450fps. Damn high, but when a full load is shot the fps looks to be more around 300. I could increase the psi, but it probably won't help much and the gun will just use more gas.

Edited by filipinofreak, 02 November 2008 - 05:10 PM.

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#5 Fatboy 589

Fatboy 589
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  • SOA Name: Fatboy 589

Posted 02 November 2008 - 10:26 PM

I was thinking about a gas shotgun, and still am, so if I ever get one, definitely going to try and do something like this. Brilliant idea.

Edited by Fatboy 589, 02 November 2008 - 11:18 PM.

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ohai

#6 filipinofreak

filipinofreak

Posted 03 November 2008 - 02:42 AM

QUOTE (Fatboy 589 @ Nov 2 2008, 05:26 PM) <{POST_SNAPBACK}>
I was thinking about a gas shotgun, and still am, so if I ever get one, definitely going to try and do something like this. Brilliant idea.


Right now I'm talking with classic airsoft guys to see if there is an easy way I could a simple hop-up to the gun. If I can figure it out, this thing will rock even more! Hopefully a hop would let me lower the psi to improve gas efficiency.
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#7 Commander Kraus

Commander Kraus

Posted 06 November 2008 - 04:59 AM

QUOTE (filipinofreak @ Nov 3 2008, 04:42 AM) <{POST_SNAPBACK}>
Right now I'm talking with classic airsoft guys to see if there is an easy way I could a simple hop-up to the gun. If I can figure it out, this thing will rock even more! Hopefully a hop would let me lower the psi to improve gas efficiency.



You could cut a hopup hole in the barrel just nest to de aluminium spacer.

Then glue a piece o neoprene o other soft rubber and put an oring over it ot add some tension to the hopup rubber to increase it effect.

That was what I did to mine and it is working fine. Im getting 150-160ft flat range with greengas. a-thumbsup.gif
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#8 Fatboy 589

Fatboy 589
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Posted 06 November 2008 - 05:25 PM

Holy hell, 150 - 160 feet? Are you serious?
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ohai

#9 Commander Kraus

Commander Kraus

Posted 06 November 2008 - 05:51 PM

QUOTE (Fatboy 589 @ Nov 6 2008, 07:25 PM) <{POST_SNAPBACK}>
Holy hell, 150 - 160 feet? Are you serious?


Yes, of course.

with a full charge of green gas and 0.25 bbs range goes from 133 feet to 160 feet max.
Remenber this shotty fires a single bb at 500 + fps, it is very powerful.
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#10 zane

zane
  • Gender:Male
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  • Interests:Firearms<br />Airsoft<br />Video games (Xbox 360 owner)<br />

Posted 03 December 2008 - 10:39 PM

Thats awesome. I have the same gun and really want to be able to fire off all 24 shots with power but my field has a limit of 300fps. Just wondering if anyone knows how I could modify my M500 for all shots but shoot under 300 fps.
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#11 STRYKER13

STRYKER13
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Posted 11 December 2008 - 03:17 PM

You could cut a hopup hole in the barrel just nest to de aluminium spacer.

Then glue a piece o neoprene o other soft rubber and put an oring over it ot add some tension to the hopup rubber to increase it effect.

That was what I did to mine and it is working fine. Im getting 150-160ft flat range with greengas.

I need to see some pics of this mod,got any? Thanks
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#12 Nodaisho

Nodaisho
  • Gender:Male

Posted 16 December 2008 - 09:15 PM

What kind of spread do you get with this thing? I've heard as much as 5 feet at 50 feet, another saying 3 feet, and that is a bit more than I would want, that seems like a bit much to reliably hit someone in woodland.
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'Ah, but who watches you, your grace?' said the inspector, with a brief smile.
'I do that, too. All the time,' said Vimes. 'Believe me.' -Thud

#13 Rob Feature

Rob Feature
  • Gender:Male
  • Location:Chicago, IL

Posted 14 January 2009 - 07:51 PM

I really want to know about the spread too. The point of the gun is that it spreads out, increasing your chance of a hit. The spread must be tighter.

Don't get me wrong, that rig you made is freaking awesome. I'm super jealous. I always wanted to do something like this with a Maruzen 870. When I saw an m500 on the cheap though, I jumped on it.

I wonder if you could mod your to put out more bbs per shot. It'd be sweet to go for a full 9(I think that's how many pellets 12 gauge 00 buckshot packs) bbs per shot.

Edited by Rob Feature, 14 January 2009 - 07:53 PM.

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I enjoy long walks on the beach, theatre, and grossly impractical airsoft guns.

#14 filipinofreak

filipinofreak

Posted 13 February 2009 - 02:50 AM

Ok, so I did a few more mods to the gun. I broke the trigger guard during the modifications, oh well. I'll probably pick up another one eventually. No pics right now, maybe I'll ad some later. Just posting the info for others.

I added a real steel ATI pistol grip. It fits perfectly, but the bolt that came with my pistol grip kit didn't fit. DO NOT USE IT. The real steel M500 uses different threads to the airsoft version. The ACM M500 uses an 8mm x 40mm bolt.

The spread of the shot is about two hand-widths sized at 80ft. But it drops almost a foot by then. The range is really bad with this gun. Good spread for CQB, not so much range for field use. The last 2bbs of the 5bb spread always seemed to drop extremely rapidly compared to first three. Makes them useless when actually trying to hit something far away. I wanted a way to load only three bbs per shot. What I did was get 7/32 brass tubing. Expanded it with a center punch until it push fit into the loading mechanism. Then I trimmed it so that it would only allow 3bbs to enter. Now the gun fires only 3bbs. Chronoed with .25g at 120psi:
-5bbs, 272fps
-3bbs, 328fps
-1bb, 439fps
The decrease in the amount of bbs the gas needed to accelerate resulted in a gain of fps. The trajectory was also much more level. A hand sized 3bb spread at 80ft with a 1-2 inch drop. The spread is less than that of a M3 Super 90. Which, in my opinion, is better since the M3 spread is too wide. I also figured out how to add a hop. First I'm gonna try the cut a thin notch and o-ring method. If that doesn't work, I'll do the more complex barrel collar with bigger notch and neoprene way.

Once again, this shotgun has plenty of potential. It's good out of the box for CQB, but not for field games. Definitely go for the pistol grip version though. More practical and maneuverable.

Sorry for the lack of pics. I'll get some when I work on the hop-up mod.

Edited by filipinofreak, 13 February 2009 - 02:58 AM.

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#15 Fatboy 589

Fatboy 589
  • Gender:Male
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  • SOA Name: Fatboy 589

Posted 14 March 2009 - 11:16 PM

I was hoping to get one of these eventually and run it in a scabbard (pistol grip, full stock would be a pain in my censored2.gif) in our woodland field. It's not that far apart, so maybe it will preform good.
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ohai

#16 Juan Ricardo

Juan Ricardo

Posted 10 May 2009 - 10:02 PM

Could you do a more detailed walkthrough of that? With prices and the sources for the parts? I don't actually own an ACM, but its something im looking at, and this looks like a killer mod. a-thumbsup.gif
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#17 Murph9935

Murph9935
  • Gender:Male
  • Location:California

Posted 16 May 2009 - 12:36 AM

Is the gas usage really that bad? I heard in one review that it was about a 30 second fill for the gas and it lasted for all the mag tubes.

I've also heard these are supposedly made by BE.

Edited by Murph9935, 16 May 2009 - 01:34 PM.

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#18 Rob Feature

Rob Feature
  • Gender:Male
  • Location:Chicago, IL

Posted 16 May 2009 - 12:14 PM

Does anyone think there's a way to conceal the CO2 rig in the stock of the shotgun? I really don't like the idea of an external air rig, but I wouldn't mind the extra weight in the gun.
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I enjoy long walks on the beach, theatre, and grossly impractical airsoft guns.

#19 Fatboy 589

Fatboy 589
  • Gender:Male
  • Interests:Skateboarding, Jesus, airsoft, real steel guns.
  • SOA Name: Fatboy 589

Posted 16 May 2009 - 10:14 PM

The weight in the gun would SUCK. I'd just keep it in a back pack or something.
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ohai

#20 dlrevan13

dlrevan13
  • Gender:Male

Posted 16 May 2009 - 10:35 PM

QUOTE (Rob Feature @ May 16 2009, 11:14 AM) <{POST_SNAPBACK}>
Does anyone think there's a way to conceal the CO2 rig in the stock of the shotgun? I really don't like the idea of an external air rig, but I wouldn't mind the extra weight in the gun.


That is an awesome idea. I don't think the weight would be too bad. The biggest issue would be getting it in there. I think the tank would be too wide to fit in the stock.
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#21 Rob Feature

Rob Feature
  • Gender:Male
  • Location:Chicago, IL

Posted 26 May 2009 - 10:30 PM

What if you used a 9oz tank? The stock buttstock is a little short. I wonder if the real steel fixed stock or fixed stock w/ pistol grip would be easier to rig up.
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I enjoy long walks on the beach, theatre, and grossly impractical airsoft guns.

#22 airsoft159

airsoft159
  • Gender:Male
  • Location:St. Louis, Missouri
  • SOA Name: Steven Kelley

Posted 27 May 2009 - 08:27 PM

QUOTE (Rob Feature @ May 26 2009, 10:30 PM) <{POST_SNAPBACK}>
What if you used a 9oz tank? The stock buttstock is a little short. I wonder if the real steel fixed stock or fixed stock w/ pistol grip would be easier to rig up.

Or a folding stock.

The tank would have plenty of room.

Maybe something like this

http://www.cheaperth...om/23868-1.html
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#23 tombo131

tombo131
  • Gender:Male
  • Location:Columbus, OH

Posted 24 June 2009 - 10:16 PM

Know what else would be amazing - use an HPA tank so that temp. is not an issue, now hook up that rig to a gas sniper rifle mag and you finally have a consistent shooting gas bolt action.
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#24 Fatboy 589

Fatboy 589
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  • SOA Name: Fatboy 589

Posted 24 June 2009 - 11:29 PM

Hey man, try to watch the necro posts.
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ohai

#25 mardivdoc

mardivdoc

Posted 25 June 2009 - 12:06 AM

How much did it cost, where can I get these parts, etc? I want to know everything, I've been wanting a classic style airsoft gun and this is the easiest way to do it it seems, nd I've got the same gun so this is perfect. Thanks man, this will be a great project.
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Proud shotgun user.

#26 T-BONE

T-BONE

Posted 09 July 2009 - 01:46 PM

QUOTE (filipinofreak @ Feb 13 2009, 03:50 AM) <{POST_SNAPBACK}>
I added a real steel ATI pistol grip. It fits perfectly, but the bolt that came with my pistol grip kit didn't fit. DO NOT USE IT. The real steel M500 uses different threads to the airsoft version. The ACM M500 uses an 8mm x 40mm bolt.


I have the tac star pistol grip on mine and the bolt fit perfectly fine.


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If you have any shotgun questions PM me, I will be happy to help!




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