Recoil Shock Upgrades – Part 4

While I don’t have many photos to go with this long block of text, I do feel that the following is worth sharing for those who are interested.



I recently was in contact with a newer player who emailed Overhoppers in regards to advice on upgrading his Marui Next Gen Recoil Shock M4. Note that some text has been removed for brevity’s sake… because otherwise it’s just too long, even for my usual long-winded explanations on this stuff.

“I was referred to you guys by Stealth on the ASC forums regarding some questions I had about the TM NGRS system.

I recently acquired a Marui M4 CQBR. I knew going in that the FPS would be low which is fine, it’s primary use will be as my CQB primary this winter.
I’m curious for next year though how it can compete in an outdoor skirmish, which is mostly the game type I play. I’m desperately hoping that I can upgrade the spring to somewhere in the 340-350fps range so it is still suitable for CQB while still having a shot at competing with the 400 fps flathopped guns and long sight lines at my usual outdoor game.
Am I dreaming? Will I need a full internal overhaul and bump to 400 fps to play with it outside?
I don’t want to mess too much with the TM “synergy” if I can help it, but any upgrade suggestions are welcome.”

It really depends what you want out of the system – there are a few ways to try to reach this solution & how you get there is up to you (bear with me, this question has a complex answer that I will have trouble keeping brief).

I’ve found that swapping springs on my personal HK416 “DG” isn’t all that bad so long as you have a small Phillips driver & soldering iron on hand. While the process is not as fast as dedicated quick change or split gearbox designs, it is still much faster than working on V2/V3 AEG by far. This is an option for you if FPS alone is the desired goal. Myself, I’ve decided to leave my HK416 “DG” with the original Marui spring – being that the HK416’s are likely a limited run & that I do have a use for a low FPS AEG anyway (CQB as well @ 330 FPS max here), that was my own decision on the matter.

Now, I’ve read that a number of TM Next Gen users out of the UK are dumping in Orga products at the cost of a couple FPS – Orga widebore & cylinder set paired with hop mods are apparently giving even the likes of Systema PTW’s a run for their money according to what some are reporting. Minimal amount of screwing around with the original Marui “magic.” This is an option as well, though I do have to admit that I have not tried this solution in either of my Next Gen’s yet.

As to my TM SCAR-H, I’ve since gone close to all out on it; though the results are still not quite what I’m looking for and are going to result in me fully doing up the internals in the end. As my envisioned end product was predominantly based on too much playing with my Systema PTW – I wanted all of it: FPS, trigger response, reliability & effective range (in that order of importance). But of course, this introduced a whole bunch of reliability concerns, for which I will explain my thought process on next…

Currently, I’m running a spring out of a China made clone gearbox assembly that I would estimate to be just under a M130 – of special note with the Next Gen’s is that the spring is shorter than standard AEG springs, though they are the same diameter. This does mean that standard AEG springs can be cut down & processed to function properly in a Next Gen.

In order to prevent the gears from breaking due to the higher load, I’ve upgraded the gear set to a Lonex. I also own a SHS set and that is currently in my HK416, yet I would still recommend spending a bit more on a better gear set as the SHS cut isn’t all that great (doesn’t look as nice as their more popular AEG gear sets). My original Marui gear set was already showing signs of wear, the material & coating definitely reminds me of that used on Hi-Capa hammers – won’t last forever, but likely for a very long time if everything else was left stock.

Higher tension spring also means more risk that the plastic bushings are going to deform sooner than later – I ended up with a Magic Box set, much to the dislike I have for Magic Box parts. They are what I feel is an inferior product at a premium price. Bushings are cheap, but if you want to go even cheaper I’ve read that you can sand out the 5.9mm bushing holes in the gearbox shell to 6mm. The oil grooves in the Magic Box bushings are already putting wear onto my Lonex gear axles, I’m not sure if I would recommend them to anyone else because of these.

Last major concern when it comes to FPS upgrades based on the spring was the plastic spring guide. I had trouble figuring out which model fits in a SCAR and so it took a bit of trial and error. As it turns out, V3 don’t work, but V9 do – I got a Magic Box spring guide that did the trick while I was purchasing bushings at the same time. Once again, I’m not impressed with Magic Box quality for the price on this one, but in this case it is just a spring guide, it doesn’t really matter if it looks good or not after the finish has worn off so long as it doesn’t break. Marui M4 of the Recoil Shock pattern are much easier to find aftermarket spring guides for locally, I picked a Prometheus one up from my workplace for my HK416.

I dropped in a custom built motor (idea comes from what some call a “Frankentorque” motor), as I wanted more torque than speed out of it – nothing like that available locally around here at that moment. While building motors isn’t something for everyone, I was impatient and wanted something to play with right away – I’m sure a comparable high torque motor would do the trick here. I’ve had less than phenomenal results with “high performance” Torque/Speed motors when running higher FPS springs. Besides, this build was supposed to be more of a “DMR” platform that would be run on semi auto to limit my rate of fire with the TM low caps – but that’s my personal preference.

The 7.4V 1300MAh 20C LiPo I was using before with the stock spring wasn’t quite cutting it for the trigger response that I’m used to (I shoot quite a bit of GBB & PTW), so I decided to go 11.1V LiPo. Seeing as how replacement Marui switch assemblies are hard to find with Marui being Marui and all, a MOSFET seemed appropriate. I was ideally looking for something that used a microswitch (replace original switch assembly) and didn’t have any other chips hanging off it down the wires as the SCAR folding stock put a serious limit on available space & wire routing options. I first saw the Big Out option on a Japanese blog, but it is quite expensive – much more than I was willing to spend. I later discovered that BTC produces one as well, though in typical BTC fashion they don’t have any in stock. A temporary solution for the time being is to install another MOSFET – though I own many Gate PICO, my biggest concern with running a semi-only gun is heat build up (heat can kill a couple of things, one of which can be the MOSFET) and the lack of a heat sink made that too big of a potential issue. I’ve since wired in a APS MOSFET with heat sink and fuse & dumped it where the Marui fuse used to be (believe it or not, the tech department of the retailer I work for has had surprisingly good results with experimenting on the APS MOSFET units – they are built very well). This solution probably won’t work for rear wired M4 models, as space is at a bit more of a premium where the original fuse is inside the stock.

One of the other writers on Overhoppers, “Dizzy,” had told me that on his previous TM M4, he managed to strip the piston quite quickly using a Lonex A1 & 11.1V LiPo – most likely due to increased torque or speed, but he wasn’t really sure. I myself decided not to take a chance on this in my SCAR project, and installed a Prometheus Piston (very hardy pistons, these have a reputation for outlasting most of the older tuned AEG around here in BC). Being that the Marui original piston head is not ported, and attaches to the piston body differently than most aftermarket piston heads, I decided to change that while I was at it too – Prometheus Piston Head, ported and with bearing to match.

For me, that’s what it took to ensure I achieved my goals for my Marui SCAR-H build. From there, air seal/compression parts help consistency, which in turn helps push your effective range further (same concept as when modding any other airsoft gun). Barrel & hop up in conjunction with BB weight can help maximize the potential of your set-up (same concept once again). Nothing different here for upgrading the rest of it; this information is generally pretty well understood & documented, but if you want my opinions on these, I can offer my suggestions to you as well?

Depending on what you want out of yours, you may not need to go as far as I did… but then again, I find that many airsoft players enjoy the upgrading process as much as the guns & the game itself, myself included.


2 responses to “Recoil Shock Upgrades – Part 4

  • Daniel Wong

    Good review.

    I skirmish in really weird places (where I am we have this stuff called iron sand, which is magnetic, and conductive), and it can get everywhere in a mechbox. On top of this is the area I am in has strange geomagnetic interference as well as strange weather patterns. Hence MOSFETs are known to be disposable.

    I just bought an M4 next gen and using a 7.4v 2000mah, Systema Magnum, SHS gears and a shortened M120 I am getting around 450fps. Here is the catch: It has lockups at the release point if I release the trigger before the cycle finishes. I do want it going at 450fps but I have been forced to cut the spring down to 400fps. Aside from using 11.1v which will fry the contacts, and I can’t use MOSFETS, are there any other things like torque up gears which can improve the pull?

    • juicy

      Depends how you shoot. Lots of semi-auto & a high discharge LiPo won’t be good for your contacts no matter what.

      To prevent lock ups without a MOSFET unit that does sector gear monitoring/cycle completion, you could try bumping up your motor to something higher torque. Systema Magnum’s aren’t bad in that department, but you can either buy something with more torque or mod it to achieve that – maybe a JG Blue for an off-the-shelf motor (known for their high TPA), or build your own “Franken-Torque” as is common for DSG AEG builds.

      450 FPS is doable, but I have my reservations about pushing any of my NGRS AEG up to that – mostly due to concern about the gearbox shell durability and relative difficultly sourcing replacements. I haven’t seen a documented Next Gen running at that FPS on the interwebs before, so while I know it can be done (I had my SCAR-H at 460 FPS for a couple of cycles when I first was experimenting with springs), so I’d rather not push my luck with that. Improving upon compression in stock TM gearbox will help you achieve your muzzle velocity goal but with a lower rate spring – just in case you haven’t done that yet.

      Given that you don’t want to use a FET and 11.1V, perhaps the extra torque supplied from a motor and/or lower spring rate will help reduce frequency of locks.

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