This is a simple fix that most anyone can do without much knowledge of airsoft guns. For this example I'm going to use an APS M4 but it will work the same on any single piece hopup unit and can be applied to other guns beyond M4's. Really it depends on how the hopup is pushed against the gearbox, if it uses a spring like most do then it should be possible to do this technique.

Base gun


Things you need: Really all you need to do this mod is a couple small oring's that will fit snugly over the inner barrel that aren't so big that they stop the assembly from going together. As well you might need some minor tools to get to the hopup on your particular gun, since this is a general guide I'm going to assume you know how to tear apart your own gun to the point you can access the hopup chamber and inner barrel.

Oring's and Hopup/inner barrel


Problem: On certain magazines the feed tube is further forward or backward which causes the hopup to move forward which creates an air leak between the nozzle and hopup bucking. The stock solution to this is a small spring about the size of a bic pen spring to push the hopup against the gearbox. The problem is the magazine is long and has allot of leverage which means sometimes moving the magazine will cause serious drops in FPS and consistency.

Hopup Unit pressed firmly against gearbox


Solution: So someone out there(not me) thought about using an oring as a shim more less to push the inner barrel against the outer barrel thereby pushing the hopup chamber back against the gearbox with more force. This gives you more consistent pressure, eliminates that movement or most of it that can cause a problem. I've seen this problem to varying degree's on allot of guns, recently I saw an SR25 that was a 500fps gun consistently shooting 400 or so FPS. Took a quick look and noticed it was just using a spring, added a couple orings and back to 500fps consistently. So this can be a huge compression leak that is fairly hard to find but simple to solve. I forgot to mention when typing this. This particular gun uses two orings to get the right amount of pressure. Other guns might need more or less, the key is getting gentle pressure holding the hopup chamber against the gearbox as mentioned. But two orings may be just right or not depending on the gun. I've got several that use more or less based on how sloppy the QC is, as well as brand and model. So don't just toss two one because I said so;) Make sure when assembling the upper on the lower that it's putting a snug pressure and looks like the picture of the pin hole below with a little overlap but not much.

Here you can see the step that the oring will apply pressure against.


Hopup unit with orings put on the outer barrel, you can remove the spring or leave it doesn't matter.


Hopup unit back installed in the upper.


Upper and lower back together, note there is a little step of distance the upper will have to go further back onto the lower to insert the pin. That's about right in my opinion, just enough give it doesn't take allot of force to put them together maybe 5-10lbs max.


Downsides: Really I don't see any downside to this, when shimming the hopup to the gearbox you don't want too much pressure. You want it snug, so when you slide the upper back in place you need to apply a little pressure to the upper to install the front assembly pin. The upside of this mod as well is the extra pressure on the front pin will make sure it's not going to fall out on it's own if your gun is a little sloppy.

I'm sure there are plenty of guys out there familiar with this technique, and are using it. But there might be some guys out there that haven't seen it or don't use it. In my experience there is little reason not to do this, and it can solve allot of consistency problems when it comes to the hopup/nozzle airseal.

Take care!

Luke

EDIT: Added information about how many orings to use.

I believe they are talking about the full face mesh type of mask rather than lowers.

Sent from my XT912 using Tapatalk

Hmm multicam is available since it's current issue its but more pricey.

http://www.ebay.com/itm/Gen-III-ECWCS-Level-6-GoreTex-Rain-Gear-Multicam-Jacket-L6-USGI-USED-/191633795464?var=&hash=item2c9e43a988

http://www.ebay.com/itm/Level-6-GEN-III-L6-GORETEX-Multicam-Trousers-Pants-ECWCS-Large-Regular-LR-/161798771879?hash=item25abf554a7

Those aren't lined, it's just the goretex outer layer so light like a rain coat or there abouts. So do plan layers like mentioned above. I'd really push you towards the Level 1 and 2 ECWCS Gen 3 stuff as it's damn good especially for the price.

Luke

If you hunt you can find ECWCS gortex in those price ranges, $30ish for bottoms about the same for top.

Luke

Well when it comes to cylinder volume you have two at least two variables at play at least two important ones. One is the length of the barrel the other is the weight of the ammo your going to be using. The longer the barrel the more volume you need, the heavier the ammo the more volume you need. If you have excess volume, increasing the BB weight will cause joule creep because the BB is staying the barrel longer and imparting more energy onto the BB. Basically joule creep is sort of unavoidable, if you've got enough volume to shoot the heavier ammo it's going to chrono lower with lower weight IE .2g BB's. If you don't have that setup then your undervolume which is also possibly a problem.

So all of that done I'm not honestly sure the best way to test that, there are allot of theories on how much volume is required, and how to calculate it. But from what I've seen and heard over volume really doesn't effect accuracy all that much if your fairly close to where you should be. It will be louder at the muzzle if you have too much volume, you'll hear more of a pop when the excess air exits the muzzle. I'm running a VSR10 G-Spec and it's hard to get more overvolume even with the .43g BB's I'm running I've only got a 303mm barrel and a cylinder that with that weight would be about spot on at 400mm. So it's very over volume but it's also pretty dang accurate and ranges past 100 yards.

For your build depending on brand of m130 and air seal that shouldn't be a problem at all, actually I'd start with an m120 for your FPS goal since I think an m130 is likely to overshoot it if you've got a good setup behind it. My M14 is running an m120 spring with a 550mm or so barrel and it's currently shooting around 440 or so. I expect it will tame down a little over time but it's pretty hot shooting right now for an m120. I've also got an M16 DMR project I've been building with an m130 in it and now that I've got the air seal coming together and working the bugs out it's shooting a pretty consistent 460-470fps with .2's and that's with an M16 length barrel. I'm actually likely going to drop an m140 in that gun to bring it up a touch since my goal with that rifle is 500fps.

On both of those guns they are full cylinder guns, I did put a ported m4 cylinder in the m16 at one point but the FPS dropped indicating it's under volume. AEG's don't have nearly the volume to begin with of a bolt action so I run the theory especially for a DMR that you almost always want as much volume as you can get IE full cylinder on any longish barrel accurate platform. Since you're going to be running heavier BB's, you'll need as much volume as you can get to really fling them out there. For that matter my M4 with 363mm barrel is also running a full cylinder from another longer barrel I tested in it, and I honestly can't see a difference in accuracy or FPS in there. It does a little better with heavier ammo because of the full cylinder but otherwise it's not a big deal.

So short version toss in a full cylinder it will give you more ammo weight options without going under volume, and should work better in just about any DMR platform. Maybe a short barreled say A&K SR25 with the extended gearbox you might need to port, but really most of those are longer platforms as well so likely full cylinder there.

Take care!

Luke

Hey guys I added a calendar which is accessible through the top links, you can now look through there and find events, click on the name of the event and it will take you to it's thread in the events section. You can still get to events the normal way as well, but this might make it easier to see what is running when rather than looking at each event title and figuring it out.

Only mods will be able to add and edit events. If someone is posting an event that isn't a mod, please just send a PM to one of us to add it for you to the calendar.

Take care!

Luke

EDIT: Well guys I've had some success many hours into today fiddling with this project. I've tried around 10 different high caps at random in this gun, all sorts of brands I've got allot of them from TM, CA, to newer stuff. Either way on a whim I tried an old Star 30 round low cap, and the dang thing fed consistently and fps was +-2. It was a smidge low around 403 where I was seeing some 430's but it's 100% consistent. So I dug around tried some other mid caps and found another original generation G&P midcap that feeds and is 100% as well. So I have some sort of mag related issue that doesn't make a bit of sense to me. These same mags just for reference feed in every other M4 gun I've got around without any issues and they run the gamut brand wise as well.

So rather than my long question below which I'll leave there in case it might help someone seeing my issue in full and having any ideas. So now I'm curious to guys that have dug into mag compatibility problems and their solutions. What is actually causing the issues, is the hopup not pressing the release on the mag fully, too much pressure too little? Just curious what you guys have found, this is honestly the first time I've had mag issues with any of my m4's over the years. I used to only run TM mags so that could be part of it, but I'm wondering if anyone else has dug into it. I'm curious at this point but I'd also like to be able to correct this issue so I can use any of my mags as well.

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Well guys I've been working on a project for a while now basically a DMR M16 built from bits and pieces. I got a bunch of random parts and threw it together but I've been having problems and honestly I'm out of ideas of what could be causing this issue at this point.

So first I'll describe what it's doing. Random feeds probably feeds BB's 9 out of 10 shots maybe a bit higher but FPS is down in the 100-200 range most of the time with an occasional full speed BB at around 420fps with .25's. Hopup of course is all over the place because the velocity is all over.

Parts, metal body upper and lower don't know the brand but the fit together is fine, same goes for stock, and outer barrel. I've got a G&G plastic hopup chamber I was trying to get to work but once these problems started I suspected the hopup unit was the cause so I went ahead and bought a ZCI unit, but the issue still is there. I've tried several different buckings, several hopup chambers and same basic results. A few buckings gave me more misfeeds but I think it was how tight the lips were for feeding. I wasn't sure what nozzle came with the gearbox I picked up used so I thought despite the specs being on length wise I'd replace it also with a ZCI nozzle since it would match the hopup unit hoping for good results. Same thing. I did put an M140 spring in here along with an upgraded motor, cycle rate is good but I don't think it's fast enough to cause any issues, especially with that heavy of a spring. I replaced the tappet plate with a new SHS tappet plate. The other one I had was slightly too thick causing some issues or I thought. After thinning and fighting with the old one I decided it might not have been putting enough forward pressure on the nozzle to feed properly and seal but the same issue was still there. Spring on the tappet seems to be strong doesn't seem any different than any other version 2 boxes I've had apart over the years. Tried several barrels with the same results. I forgot to mention above the hopup unit is shimmed with orings to the geabox and it's got a fair amount of pressure against the box and should have a good seal.

So I'm looking for suggestions, I've been reading and racking my brain trying to come up with possible causes and honestly thought I had it on the run today with the new nozzle and hopup unit, but alas same issues again. So ideas would be more than appreciated, particularly if you've seen this issue or something like it and other things I can try.

Take care!

Luke