So I have this Optac 400mm barrel that I bought for an M4 build. I’m wondering if it would work for my new G28 which originally came with a 440mm barrel?
Rok currently has a build underway, for my HK117.
All a bit of an experiment…playing with the V2.5 gearboxes…
Given we can get 400 fps out of V2 builds…the whole point of larger volume V2.5 gearboxes, seems to be to match larger volume, to a longer barrel.
The holy grail, is trying to get High fps, with better range and accuracy…supported by a longer barrel.
How easy this is to achieve, remains to be seen.
Vipertac had a modded V2.5 blaster… 390 fps, good hopup… and was getting good accuracy, at a range over 40m.
Freak build.?
I hope not, and hope that its reproducable…
Lets see if longer barrels contribute to better accuracy…
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So my theory… a normal V2 with good seals and full stroke does start to run short on volume around 380-400mm barrel- depending on cylinder and nozzle.
Normal V2 short 3 teeth does similar for around 275-285mm barrel.
Will this scale up to a 450-500mm barrel? I don’t know… yet! Peak acceleration of the gel is at the end of the barrel… and you’d like to think at that point it is at its most stable… then it hits the hop up!
Hard to say but I’ll be finding out soon enough!
The extra travel of the piston, length of stroke also means (at least from what read in some airsoft forums) you generally lose a couple spring ratings.
ie you’ll need an m120 to get m100 power (airsoft frequently used an M140 to get M120 power for their DMRs)
I feel the main benefit of the extra volume is just that… more volume to run a longer barrel.
So it’s gonna be fun to find out.
I liked BME’s so much that when I seen one going second hand I snapped it up lol.
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Old Doc Bob Nylon Gen8 powered 350mm barrelled builds cranked 400-430 FPS without any issues…,… other than fkn AR latches 
But anything beyond 400mm 7.5mm barrel really stretches the capacity of a 100% cylinder to be able to power anything until using smaller “tight bore barrels” to reduce the volume required.
And who says you don’t like E&C…!!
I’ll try both and run it through the chrono. If I use this Optac barrel I’ll have to find a grub screw that sets the height while flush. Otherwise no pokey pokey. I’m kinda inclined to order a 500mm and cut it so the hopup sits in the flash hider instead of the outer barrel. That would give me another 2cm or so.
That is basically what I am doing for BMEs and mine (when it comes).
Will be good to see your results alongside with mine.
Always love seeing some new stuff getting love.
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You could try a sliver of coke can and slide it in-between the hop tongue and the barrel. Push it down far enough until you’re happy then cut it off so that it eliminates the need for a grub screw.
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I’ve got a few of those… you’re only ever going to get a thread or two of engagement with the shortest grub screw.
Fortunately all of mine haven’t needed a grub screw at all to get the right amount of hop, so none of them have one.
Jug’s shim method will work, there’s always the chance it could rattle out though… but then you just shove in a new shim. 
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So in preview to a future video… M120 in the M110A1… is just over 400fps… I suspect it will settle a little as my BJX springs do start a touch hot, then “bed in” slightly. It will very likely be around the 400fps mark still though.
I have two integrated hopup barrels to try… the first seems to be like any “DMR” powered blaster… 1 of 5 is pretty good, the rest are a little erratic. I haven’t tested with the harder summer cat green and orange yet though as I had none ready. Also no sorting was done.
It did make some pretty impressive distance… and when the hopup and gel gods aligned it was impressive.
More effort needed to see how it goes!
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So looks like the gearbox is coming apart. Nozzle isn’t retracting fully and gels aren’t feeding well. Velocity is way down when it manages to fire. I swapped to the m120 so I can’t really claim warranty. But can’t think of anything I did that could cause the nozzle to not fully retract and really shit fps