Prometheus Flat Hop-up Tensioner Install – Part One

$30+ worth of rubber. Only in airsoft...

$30+ worth of rubber. Only in airsoft…

As per my previous entry on my Airsoft Store Canada order, I recently picked up a Prometheus Flat Hop-up Tensioner. I’ve been wanting to play with “alternative” hop setups for awhile now (“alternative” meaning other than your standard mounded hop rubber and cylindrical hop nub), so I figured, hey, why not give this a shot? The flat-hop concept has been around for awhile, but the nubs (particularly the popular Firefly flat nubs) have been ridiculously hard to find until recently, when Prometheus made these widely available.

Pics of the initial install and a quick review of the initial performance after the break.

photoThe Prometheus Flat Hop-up tensioner package consists of two flat hop nubs – the “soft” blue one, intended for sub-400fps setups, and the “hard” black one, intended for setups with greater than 400fps. I went with the blue one, as the AEG I tossed it into would be shooting around 360-370 fps. As you can see from the pic above, fitting it into the hop-up arm required cutting off both of the “fins” on either side of the rounded nub as well as trimming a little bit off the edges to ensure it fit into the hop-up window.

I mated the tensioner with a Lonex 50D Hop-up rubberI removed the inner mound and alignment ridge with a sharp knife, then sanded down both areas with fine grit sandpaper so that it was essentially a smooth sleeve inside and out. Then I rotated the sleeve about 90 degrees so that the tensioner would be acting on a smooth, “virgin” piece of rubber (lol). I slipped the rubber onto the stock VFC barrel, then slid the whole thing into the VFC hop unit. It took some fiddling to ensure the tensioner was flat, but I eventually got it right after about twenty minutes of fiddling.

photo (1)Above is the result after looking down the barrel and pushing down on the hop up arm to put some hop into the chamber. To be 100% honest I think it requires further tuning, as the tensioner tends to slant forward instead of staying completely level when hop is applied. Thus the hop isn’t as “flat” as I would like it to be, and I think I’m pretty much just getting the normal hop mound effect instead of the flat hop effect I’m looking for.

However, I decided I may as well game it anyway to see how it would do as-is. I gamed the AEG for an entire day and I was relatively impressed with the groupings and range considering the stock hop-up unit and inner barrel. I would say it shot moderately better than a stock AEG would have, but I’m not getting the groupings/range that some people online claim to be getting. Granted, they’re getting those results with Prometheus barrels and aftermarket hop-up units, so I think those two items will definitely be in my next order from Airsoft Store Canada.

I’ll fiddle around with it tonight to see if I can’t get the tensioner to remain completely flat once hop is applied – I think this will probably involve gluing the tensioner to the hop arm at a specific angle to ensure it stays flat with hop turned on.

Now that I think about it, though, I think I might just wait until I order a new hop unit and inner barrel before I do this. The AEG is shooting well enough to be competitive on the field, so I guess there’s no point in messing around with it until I have all the permanent upgrades on me.

*adds Lonex hop unit and Prometheus barrel to Airsoft Store Canada cart*

Can anyone suggest a fully metal V2 hop unit?


NOTE: I did notice a 30-40 fps increase with the above setup over the stock VFC rubber. I’m unsure of whether this is a result of a leak in the stock setup or a better seal on the Lonex rubber, but regardless it was a nice surprise.




2 responses to “Prometheus Flat Hop-up Tensioner Install – Part One

  • lupo

    I’ve switched all my AR hopup units to the Modify accurate unit. I was using a Madbull ultimate as the dial is a better design. But the Madbull does not work well with a lot of nozzles.
    I can recommend the Modify unit , it seals very well and is a solid construction. Iam also using the Modify Baton Ryusoku hopup as the rubber comes standard with no nub and the bucking is flat.
    Iam considering ordering a R-hop Z kit and using the modify parts to test with. However I currently can hit targets at +180′ using .28 fired at 285 fps (.2 @ 335fps) So I don’t know if Iam going to see any actual benefit.

  • Gunny

    Prometheus hop up unit. at $60 bucks its not cheap but i love mine. very consistent and no air leaks.

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