Deep Fire PTW-Style Barrel Kit for M4 AEG

This “Deep Fire NEW HOP-UP 14.5 inch Outer Barrel Front Kit for AEG M4 series” comes from I was so excited when I received it in the mail that I had to open up the package in my car and start taking photos of it with my phone. I couldn’t wait but get it installed at work, so a plethora of phone pictures that are most likely out of focus are as follows (after the break):


I found that the PTW hop up design does in fact perform better than what you can probably get out of a M4 hop up chamber – there is less give and flex and wobble in the parts that come together to produce hop up in the PTW than in an AEG. So when I noticed that Deep Fire had released this barrel kit a few months back, I decided that I would definitely give it a try – a PTW hop up in a tuned M4 AEG has got to perform well, right? At the very least, I’ll have a hop up that won’t be backing off on me as I play, but that is compatible with my many, many PTS PMAGs. Here’s hoping that this one actually works, contrary to some of the drum hop chambers out there, like the Madbull and Pro-Win I’ve previously tried in my King Arms.


I do order from Scopeandlaser from time to time – they often have latest parts still in stock that some of the larger Hong Kong retailers don’t have. As that store isn’t so well known, they tend to be a little bit slower to pack up and ship (I figure it is a one man operation done by Patrick there) – but they ship via HK Post in packages that are suitably sized and padded (or not), based on whatever product they ship out, meaning that shipping doesn’t cost an arm and a leg for something small like a hop up bucking.


This “new” design was actually used in Deep Fire’s older Gold series (or one of those series) AEG M4s that are no longer in production. It strongly resembles a PTW hop up design – however the chamber, outer barrel, inner barrel sleeve, and inner barrel are in fact different in dimensions and are (as far as I can tell without trying them) incompatible with existing PTW or AEG parts. Initial impressions were very good at this point in time – the machining and finishing on the barrel seemed to be very well done. Hop up chamber is obviously cast pot metal though, more on that later.

Quick note – the one I received only has a single hop up cage cushion (small rubber bit that acts as a spring to keep hop up cage from moving wherever it pleases when hop up is set at 0%; that being said, the box to my hop/barrel kit did appear to have been opened previously.







Disassembly/reassembly is very similar to a PTW hop up, except that there are a few additional O-rings here and there – presumably to ensure a tight fit and good air seal. Note that the hop up roller is not the full length of the cage – this does cause inconsistency in hop up effect applied in Systema PTWs, and I will be fixing this when I’ve got the hop up chamber properly fitted to my King Arms.









The hop up chamber has no spring at the front and thus requires a precise fit with the upper receiver in order to transfer the shock of the gearbox cycling towards the upper receiver (hopefully this works and helps prevent my current gearbox shell from cracking). It currently requires fitting to fit in the King Arms (Colt) M4A1 upper receiver, though seems to be a drop-in for the Ares. I have not yet shot through the Deep Fire hop/barrel kit, so I can’t yet confirm if it works in either, what FPS I’m getting compared to the previous hop up, how far it shoots, etc.


I was hoping that it would be a drop-in fit in the King Arms, but now that I’ve compared the KA upper receiver to the Ares, I can see why it wouldn’t be. The King Arms upper receiver has a reinforcing block (in the area where the gas tube inserts into the upper receiver) that is not present in the Ares upper. This means that with the Deep Fire PTW-Style Hop/Barrel kit installed into the upper receiver, the upper and lower receivers don’t have enough clearance to fully close as the hop up chamber is slightly too long for proper fitting in this instance.

My solution to this is to slowly file away at the material on the front of the hop up chamber until it fits snugly but properly against the upper receiver. Any wobble here (without the addition of a spring or shim) with definitely create an air leak. Good thing though, the hop up chamber is pot metal as mentioned earlier. I’ve slowly started to do this tedious process (file-polish-test fit-file-polish-test-file-polish-test… etc) at home.

Oh well, at least I finally hacked off the King Arms barrel nut – on some of these KA Colt M4A1/M4 CQB the barrel nut is impossibly tight on the upper, meaning that you can’t just torque it off without some sort of crazy machine that I definitely don’t have access to. Solution? Cut off the delta ring assembly with an angle grinder.





I guess this is where my photo review of the Deep Fire PTW-Style Barrel Kit ends – I’ll have to post a update when I’ve got it installed and working. I’ll link that update through this write-up when its up.

At the $130-ish price tag (including shipping), it better be amazing and totally worth it. I was actually considering selling this King Arms M4A1 at one point in time, however I decided to keep it due to the money invested in it and for sentimental reasons. So… I decided that I might as well throw more money into my KA M4A1. And so here we are.



16 responses to “Deep Fire PTW-Style Barrel Kit for M4 AEG

  • Goggles

    Got to let the Goggles know how this experiment goes, hmm?

  • Luke Takeuchi

    I don’t know how they keep those barrel nuts on but it’s not from this world.

    When I added my URX rail system onto my KA M4 we spent hours trying to wrench it off and loosen it with a heat gun. In the end I did the same as you and just cut it off.

    I’m curious as to why they lock it on so hard, it would make it impossible for someone to upgrade unless they had the right tools.

  • james

    Any update on this thing Juicy?

  • Evan

    I have one of these sitting around; didn’t fit in my gun (VFC), couldn’t sell it. I did try filing it, but when I got to the point that it would fit the alignment was so poor that the nozzle wouldn’t even go forward all the way.
    Other than the Ares (ew), do you know of any receivers that it drops in to?

    • juicy

      In addition to my King Arms, I also tried and failed with a VFC upper that I borrowed. I haven’t tried G&P but I’m fairly certain that it would have similar results. I did have limited success with Ares myself as well, but yeah – its an Ares, ew. I don’t currently own any other M4 AEG that I can test with.

  • juicy

    Condensed update: with a little bit of parts swapping, it now works. Long version of this update coming soon.

    • Olfs

      I’m curious about the results. I’m usig this for about 1,5 years with decent results. I’ve run into the tipical problems of ptw hop-up. With Orga flathop and a custom cusion i’m getting the best results. The range and groupings depend on many factors (each with their proportion). This over a normal flathop , i think , ofers more flexibility in adjustments when using bb’s with diferent weights.

      • Olfs

        … rhop vs this

      • juicy

        Great to hear that its working for someone out there. Mine isn’t 100% working yet, but I should be able to give it another go soon. I’ve had the darned thing long enough, may as well make it work.

        I’ve been shooting mine with both a MAG Curve roller and a custom thicker roller. Thus far, results don’t seem to be similar to that of my PTW, though I’m chalking the decreased max range up to the 6.02 barrel & some inconsistencies that exist with the current set up I’m running. Use of the Orga flat hop to help in this department sounds like a great idea.

        I’ve got consistency/feeding issues between air nozzle and chamber packing (double feeds), and am currently waiting on a few parts to try to put in there – namely a Deep Fire M4 air nozzle.

        I would also have to agree in terms of range of adjustment as compared to flat hop or R hop mods, though generally speaking I don’t find myself changing BB weight at all, once I’ve got a good set up going. On a side note, in terms of range of adjustment, I did notice that the included Deep Fire hop cage has less adjustment range than any of the other cages I own.

      • Olfs

        For the nozzle compatibility you could consider dremeling the chamber of hop (the side by the gb) or the upper. Also you can manufacture some washer/s (front/back hop chamber) for better positioning. I’ve done all the above on two of my replicas. Each job had it’s particularities.. I’ve used mag curve roller with fcc spring and had good results with 0.25’s.(0.3’s created some sort of vibration).

      • juicy

        Hmm… Double feed/loss of compression is likely due to air nozzle not reaching all the way to chamber packing lip. Makes sense, good idea. I attempted to use longer M4 nozzles, i.e. SHS red being the longest I own – compression still not there. Another idea to get the nozzle sitting further forward would be to shave the front of the tappet plate – but depending on how much material you removed from the back of your chambers, this may not be enough; your thoughts on this?

        I have tried O-rings to jam the unit as far back (towards the GB) as possible, but the results I have now are the result.

        Inconsistencies could be due to the FCC spring – theory being that because of spring shape, it can allow for wobble. Orga has recommendations on this posted somewhere, though I know he isn’t the only one.

      • Anonymous

        You can make an ideea of how big the gap is by putting a flashlight at the end of the innerbarrel and watch lighted area near the tip of the nozzle. Regarding the shaving of the tappet plate i think it can give just a little gain but it’s a moving part that’s under stress , i prefer not to do it.
        Here is a link to an exemplification picture about the intervention to the hop-up chamber :

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