Lonex M4/M16 hop-up unit

[Stealth]

So as part of the build-off I'm having with John on a VFC HK416 CQB, I decided to test out just how good the VFC hop unit was compared to some options as well as install a PDI W-Hold rubber. I feel like hop units are often overlooked as it can be a large source of airleak and potential barrel instability.

Let's start with the stock VFC unit. It's completely plastic and features a special proprietary anti-rotational C-clip that retains a lot better than traditional clips. Nice touch. A metal stabilizing ring is also included and the wheel design is bit different than traditional units and makes it easier to adjust if you have gloved hands. Same cheesy small spring up top though.


Removing the clip took a bit of effort with a small screwdriver, but once removed the rubber is exposed. A fair amount of silicone oil/grease is used but the rubber slides in and out of the unit relatively easily without jamming up the sleeve. Barrel was fairly dirty though:


Next I tried to install the PDI W-hold hop rubber with a dab of 70wt silicone oil into the VFC unit but due to the softness of the PDI rubber it tends to stretch longitudinally if it's too tight. The result is a rubber that's too long to accommodate the C-Clip. Note that the notch in the barrel is partially obstructed by the rubber.

More oil didn't seem to help the situation. Rather than trim the end of the rubber, I turned to the Lonex hop unit.

The Lonex hop unit is plated (zinc?) just like their gearbox shells. This means that all working surfaces are very smooth - key when installing the PDI rubber here. It also features an o-ring at the rear of the unit - presumably this helps to create a perfect seal between the mechbox and the hop unit itself. Assembly is just like any standard hop-unit - why re-invent the wheel?

I was able to wrap the PDI rubber with some teflon tape and slide it into the unit with very little effort - too easy and it's going to have an airleak, too tight and the rubber will stretch out. 1.5 winds of teflon tape was optimal for my setup.


Barrel with rubber installed perfectly and as you can see there is room for the C-clip to seat correctly.




As with all my builds - I didn't bother with the little spring up top. I simply used a stack of rubber o-rings (the orange things) from McMaster-Carr to properly shim my barrel up against my mechbox to ensure a perfect seal everytime. Didn't use an HS5 barrel shim, just used a metal ring this time.

Testing results (fps readings averaged and rounded over 10 shots)
Original VFC hop unit with VFC rubber. FPS = 345
Lonex hop unit with PDI Rubber. FPS = 351
Modify hop unit with PDI Rubber. FPS = 331


Conclusion:
Seems like the VFC unit is not too shabby out of the box and the anti-rotational clip is a really nice touch. But because it doesn't accommodate the rubber I wanted to use, I'll just save it for another setup. The FPS gain between the VFC and Lonex unit may be attributed to an improved seal and/or the tightbore barrel used with the Lonex unit.
FPS loss via the hop-unit is unacceptable to me - if I'm putting in an M130 spring and subjecting my gearbox to those forces, I expect the system to give me the full power it produces.
I also tested the whole setup with a King Arms hop-up but the fps variation was so nuts I just tossed the damn thing.


Want one? Can't have it, we're out of stock temporarily. I actually want more of them for myself for other builds...

[M.Garcia]

So in your opinion based on what you have here, would you say Lonex has the best hop up assembly for M4/M16?

[Stealth]

Comparing between the following (since this is all I have):
King Arms Enhanced metal
Modify Enhanced
VFC stock plastic
G&G stock plastic
King Arms stock plastic
G&P stock metal
Systema Enhanced metal
Madbull 3-in-1 Ultimate

The 2 that come close to the Lonex in terms of raw performance (FPS and consistency) are G&P and Systema. The rest aren't as good.
G&P gives me good results but their machining isn't nearly as precise as Lonex. Systema is made well but I'm not not huge on the painted finish that Systema uses.


Some notable ones I haven't tested:
Prometheus Neo Strike
SHS
Prowin

[Rabbit]

Pretty sure my brother grabbed the last one off you on my recommendation like 2 days ago Website says they're still in-stock tho.

Your testing concludes a raise in FPS - personally I want to see a range comparison.

[Stealth]

Originally Posted by Rabbit

Pretty sure my brother grabbed the last one off you on my recommendation like 2 days ago

Your testing concludes a raise in FPS - personally I want to see a range comparison.

It's not really a RAISE in FPS. just that the other units were leaky to start with.

I would do unspeakable things to have access to a wind-less, private indoor 250+ft range

[NS-Airsoft-Noob]

I just ordered a Lonex hop-up unit from Airsoft Store Canada; hopefully it yields improved performance over my stock plastic one-piece CA Sportline unit.

[Rabbit]

Picked one up from airsoftstore.ca - Paired with a purple prometheus hop up sleeve and I had bbs dripping out every second shot

Put my stock cyma hop up back in with the purple prommy and everything was flawless.

When pushing the Lonex unit up againts my airnozzle (with the top receiver off) it all of a sudden felt like my nozzle wasn't long enough to engage (or kiss) the hopup sleeve/inner barrel combo inside the hop up unit

Thoughts?

[Stealth]

Originally Posted by Rabbit

Picked one up from airsoftstore.ca - Paired with a purple prometheus hop up sleeve and I had bbs dripping out every second shot

Put my stock cyma hop up back in with the purple prommy and everything was flawless.

When pushing the Lonex unit up againts my airnozzle (with the top receiver off) it all of a sudden felt like my nozzle wasn't long enough to engage (or kiss) the hopup sleeve/inner barrel combo inside the hop up unit

Thoughts?

As with any hop unit you're going to want to check the nozzle/hop rubber interface. With the hop unit pressed up against the mechbox, shine a light into the feed hole and look through the muzzle - do you see light? If you do then the rubber is not a good match for the nozzle.

Also, some rubbers work better in certain hop units and barrels.
For example - I found out that PDI rubbers don't work with Lonex barrels. I was getting 330fps. I switched to a Lonex 50D then got 505fps. Go figure. At least I know Lonex hop unit + Lonex rubber + Lonex barrel = ideal.

It sucks but it's the reality when you're mixing manufacturers, nothing is for certain. All kinds of factors come into play such as the bevel of the end of the hop unit, bevel on the barrel, angle of the lip of the hop rubber, etc,.

[Stealth]

Bit of an update - I find the new batch of Hop units to have slightly oversize hop arms. I had to file down each side of mine to get proper operation out of the arm.

Not a huge deal but not sure why they changed it up...

[ManateeMatt]

I am sure its been covered before but what 5 o-rings are using for spring replacement.

Edit:
annnnd if I could read the post, I would have seen it.
So never mind

[Stealth]

Originally Posted by ManateeMatt

I am sure its been covered before but what 5 o-rings are using for spring replacement.

Edit:
annnnd if I could read the post, I would have seen it.
So never mind

You have to play around with the # of o-rings depending on your hop-up and outer barrel. Most of my guns use 2.