Rotary style hop-up chambers were once relegated chiefly to the realm of aftermarket upgrades. Now it seems that many manufacturers have hopped on board the rotary train, and it’s not uncommon to see new AEG rifles coming equipped from the factory with this style of hop-up chamber.
There are some advantages to the rotary style chamber over the more conventional setups most will be familiar with. Chiefly, there are fewer moving parts; some designs entirely do away with the push-in retainer rings and all of them completely eliminate the trio of gears previously found on hop-up chambers. For pure ease of maintenance and fine tuning (especially on the hop-up arm), a rotary chamber makes a lot of sense.
Perhaps the biggest advantage is the the method by which the hop-up arm is adjusted. On most designs, the arms sit inside a graduating track (sometimes notched or indented on one side) within a large wheel which completely precludes the possibility of the hop-up arm wandering out of position as is often the case with traditional style chambers. This also means finer adjustment is possible.
In the case of a traditional chamber, there is upwards spring tension placed on the hop-up arm, which in turn works against the 3 sets of gears that are only maintaining downward pressure via friction – which is obtained by either a tight precision fit, small washers / shims or o-rings. The vibration from firing cycles can, in some non-rotary hops, cause the adjustment wheel to rotate and thereby causing the hop effect to lessen over time (hat tip to John Boycie Turrell for the phrasing on that last sentence!).
In this post, I will be covering the most popular aftermarket rotary hop-up chamber options currently available. It should be noted that these particular chambers only fit Ver. 2 guns, unless otherwise specified.
ProWin CNC Hop-Up Chamber
This particular hop-up chamber is perhaps the most popular out of this list. At one point in time it was the only option available, which inevitably lead to its market dominance for some time. I would speculate it probably still outsells all other options presently available based on being a household name alone.
The ProWin is a very simply designed hop-up chamber consisting of just 9 parts total (I forgot to insert the adjustment screw and o-ring into the photo).
There is a lot of speculation that these chambers are no longer CNC machined from solid stock, but rather cast and then CNC machine finished. I’ve read enough conflicting information on these now to say that nobody really knows except the manufacturer. As well, there have been some reports of quality control issues with the newest releases. My own experiences have been largely positive, and I’ve only seen maybe a handful of actual bad chambers in all my years of using these.
Due to the short design of the arm, and the fact that as it dials in it comes down at an angle, it isn’t necessarily the best option for R-Hopping – insofar as modifying it for an M-Nub is concerned. When using a curved spacer, such as the Maple Leaf, etc. it is allowed to follow the contour of the bucking and actually produced very favorable results. I would also say simply using a traditional round nub is quite acceptable too.
The retainer clip for the hop-up wheel is nice and positive, which is not something I can say for some competing chambers. An o-ring is situated underneath to keep the wheel from rotating of its own accord.
The one thing I personally find unfavorable about this chamber is the adjustment screw that attaches in the front. The purpose of this screw is to ensure the chamber is seated fully against the gearbox. The threads on this unit aren’t very precision, so the screw sits rather loosely in there, making some loctite necessary as it will wander out of position otherwise. As well, it can be quite tricky (and tiresome) getting it adjusted just right. My preferred method is to install the screw halfway and add a conventional hop-up chamber spring to the screw or use a series of small o-rings on the barrel instead.
On slightly related note, the nub arm from a ProWin can be used to repair a broken arm from the turd that is the APEX rotary chamber.
Average retail price is $29.00.
Madbull Ultimate Hop-Up chamber
This chamber is usually packaged with Madbull receiver sets as a standard item. It can also be purchased individually and includes the generally well-regarded Madbull Blue bucking.
It is a cast chamber consisting of a total of 13 parts, including the bucking. I would describe the overall fit and finish of the components as average at best.
The hop-up wheel relies on an o-ring placed underneath to apply resistance for the adjustment side of things. There is no retainer ring to keep the wheel attached, so it is up to the gearbox to keep the wheel from falling off otherwise. The left side of the unit features a rectangular cutout for the attachment of an optional LED tracer unit. The feed nozzle has a cutout for the placement of a small o-ring that will help prevent you from losing some BB’s upon the removal of a magazine, which is a nice feature.
While this chamber offers a lot of potential and some nice features to boot, out of all the hop-up chambers covered here, this is probably the worst of the bunch in my book. I have yet to find a single application where this chamber simply dropped in and worked 100%. There are also many cases where it won’t slide into the barrel grooves on certain guns without modification. I also find the barrel c-clip to be a rather sloppy fit, which allows for too much movement. This does not even account for the myriad of nozzle compatibility issues, of which this chamber has them in spades. I am actually a fan of most Madbull products, but this hop-up chamber is garbage.
Average retail price is $29.00.
SHS CNC Hop-Up Chamber
In many ways, this chamber is a clone of the ProWin, and borrow many of the same features with some slight design changes added in. This chamber can sometimes be found in alternative colors and is also rebranded under the Matrix label.
It consists of a total of 8 parts and appears to be fully CNC machined. It should be noted that the nub arm doesn’t actually come equipped with an M-Nub. I pulled this out of a customers gun that had been previously modified by them. The actual hop-up arm has a molded in concave nub (see below).
The adjustment wheel is retained by a decently snappy c-clip and relies on an o-ring placed underneath for friction. The body of the chamber itself features a cutout for the installation of SHS’s optional Shock Transfer System.
These chambers have been pretty hit or miss for me. On one hand, they can be a viable alternative to the ProWin, but I’ve seen my fair share of lemons. As issues go, the one encountered most is the feed tube not being machined completely through, resulting in BB’s lodging near the top.
This can be fixed, of course. I’m also somewhat ambivalent on the design of the hop-up arm. On one hand, when it works, it works great. But on the other hand, sometimes… it’s not so great.
Average retail price is $30.00.
Prometheus Wide-Use Rotary Hop-Up Chamber
A relative newcomer to the market, these are die-cast chambers that have been nicely finished out. The overall fit of the various parts is quite precise and rigid. The barrel retainer clip borrows a page from VFC and locks in very tight – which also makes it quite a task to remove too.
Total parts count for this chamber comes in at 8. The hop-up wheel is very reminiscent of the Madbull Ultimate’s wheel, and is retained by a large o-ring, which also applies a decent amount of friction. It’s actually a pretty good design from my testing.
The nub arm design is also interesting as they’ve made it so it has a slight angle. When the wheel is dialed in the nub straightens out and hits more squarely on the bucking. Much like the ProWin et al. it also works better with a concave spacer or round nub than a true M-Nub. For R-Hopping purposes, this chamber excels in this arena. The one downside that I see is there is some wiggle room on the sides of the arm. I typically have had to add two 0.2mm shims – one on either side – to center the arm.
All the positives aside, this chamber can be picky with certain guns due to its precision. Looser tolerances makes some chambers less picky, whereas this one has fairly tight tolerances. Some gearboxes need the front nozzle hole enlarged so this chamber will index fully. I’ve also found polymer nozzles to work best, such as the Guarder precision oil-tampered and VFC. Gearbox alignment has also proven more critical, and if you can get it to center the nozzle well within the chamber, it will be much more forgiving on you. With a perfect setup, however, this chamber can help deliver some awesome accuracy.
Average retail price is $40.00.
Retro Arms CNC Rotary Hop-Up Chamber
This chamber has so far been released in two generations, with the current bringing some needed improvement to the design. The unit pictured below is the current generation. They are CNC machined from a single piece of EN AW 7075 aluminum.
The design consists of 8 parts. It is the only rotary chamber I know of besides the MAXX that actually uses a spring underneath the nub arm. It is also the only chamber I know of that has an indexing nub arm which produces audible clicks. This latter point can make the wheel hard to adjust. The old generation used a checkered wheel, which was quite difficult to manipulate until the unit was fully broken in. The newest revision uses a wheel that has horizontal slots cut in, which is a lot easier to get your fingernail on and adjust. I’ve found that dropping some lube on the inside track of the wheel greatly improves the movement of the wheel. My preferred lube for this is Benchmade Blue Lube.
The threaded red collet replaces the traditional brass ring that goes around the barrel and helps center things. It’s actually a really nice design, and I wish more chambers would move to this setup.
The barrel retainer clip is a weak point here in that there is too much movement. Part of this is due to the body of the chamber having the cut for the clip too deep, which allows for a margin of slop. I’ve had better success replacing this with a G&G barrel clip.
An important caveat to this chamber is that you will have to cut around 1/4″ or so off the tail of the bucking in order to attach the barrel retainer clip. I haven’t seen a single bucking where this has not been necessary.
The hop-up wheel retainer is in a word: cheesy. Out of any of the designs mentioned on this post, it is the weakest of the bunch and scarcely holds on. I suppose it does the job, but I do not personally trust it. That being said, you can drop the clip from a ProWin or SHS and it will work good. A better alternative is to simply use a fat o-ring instead, which in conjunction with a lubed wheel track makes this chamber work significantly cleaner.
Despite some of the negatives and needing a few changes, this is still one of my top picks for a rotary chamber. It will often cure guns that are proving to be picky or problematic with hop-up chambers and it is quite forgiving on nozzle and bucking selection too.
Average retail price is $35.
MAXX CNC TE-Pro Hop-Up Chamber
The MAXX is undoubtedly the most complex of any hop-up chamber ever conceived. You can tell a lot of thought and engineering has gone into the design of this chamber and its various features.
There are a total of 23 parts and pieces (a few not pictured here), which means this chamber actually comes with a set of instructions!
The most innovative aspect of the MAXX is the hop up arms. If you elect to use one of the two provided R-Hop spacers, it becomes a Top Down Center (TDC) setup, which is quite ideal for R-Hopping. The spacers come with two different sized circular nubs, so you can select the one most appropriate for your needs.
The hop up wheel is held in place via friction provided by an o-ring underneath and is quite easy to manipulate due to the large lugs. There are a total of 3 springs – one of which is optional – that one can use to apply even pressure against the chamber. The barrel retainer clip is attaches in a positive manner and doesn’t allow for much rotation.
There is also a small spring loaded lever on the feed tube which is designed to retain your BB’s when you remove a magazine. By depressing the lever you can release any BB’s that are still in the hop up chamber. I have noted that this can make some magazines a little difficult to insert. Whether that’s from the feed nozzle being slightly too long, or some other dimensional variance, I’m not quite sure of yet.
The sides of the chamber feature 4 circular cutouts that one can cover with a pair of provided clear windows or an optional LED tracer unit. For those who are curious, the windows are optional, and the holes aren’t large enough to allow a BB to slip through. I have found that with VFC guns the windows impede the ability to slide the upper receiver on as it catches on the lower push pin lugs. By filing the bottom of the window down, you can fix this issue. Or simply don’t use the windows.
Obviously all of these features and design elements lead to a rather expensive hop-up chamber. You can expect to spend around $60 for the chamber itself, and around $75 if you purchase the chamber with the LED unit.
In some ways I feel this chamber is needlessly complex; complexity for the sake of complexity, if you will. But for the true tinkerer or guys who want a high level chamber with a lot of features and options, or someone who wants to put the crowning touch on their ultimate build, this is the way to go. It does require some finessing and tuning to get right. It’s also a bit picky with certain nozzles and buckings. The Gen. 1, as an example, was reputedly designed around the Maple Leaf bucking (which is one of my least favorite buckings ever), and that alone made me reticent to purchase the unit when it was first released. The newest revisions are fortunately more friendly with other bucking’s. For your average Airsofter who just needs something basic that works decent and isn’t mechanically inclined, all of this may be an obstacle to accessibility, however.
While these chambers have enjoyed largely positive reviews, I can’t honestly claim this to be the one chamber to rule them all. A suitably set up Retro Arms or Prometheus chamber can perform just as good in my experience. And at the risk of inciting a pitchfork massacre, even a basic non-lemon flavored ProWin can perform nearly as well if you know what you are doing. I would suggest this chamber if you want an LED tracer module and the BB latch mechanism or ever desire to easily swap between a conventional nub or R-Hop nubs without having to source extra arms.
Average retail is $59.95.
Nub Arm Comparisons
Below you can see a side-by-side comparison of the nub arms from the various hop up chambers featured here. Again, the SHS arm isn’t actually correct as it had been previously modified by a customer. It’s just what I had on hand to use for this writeup.
