G&G CQD low FPS

[tunabreath]

Alright, I can't figure out for the life of me what's going on here. I'm losing about 50-80 FPS.

In an otherwise stock G&G CQD, here's what has been replaced:

Element piston
Modify piston head (POM)
Sorbo pad
Modify nozzle (POM)/original nozzle
Madbull ultimate hop up unit
Firefly soft bucking
Modify S120+ spring/VFC SCAR-H stock spring

The S120 should be giving me about 410 FPS, and the VFC stock spring should be 360 FPS (chronoed in other guns).
Instead, I'm getting 330 from the S120 and 315 from the VFC.

Compression of everything inside the mechbox is perfect.
I'm thinking the issue is between the nozzle and the hop up. The hop up tangs have been filed down and the unit is able to slide with the spring that keeps it pressed against the mechbox.
Switching nozzles has caused absolutely no change (the Modify one is slightly more tapered at the end than the stock one)

If the issue is what I think it is, then I'm probably going to try this:
http://www.airsoftcanada.com/showthread.php?t=92666
The thing is, when shining a light down the feed tube, I can't see any light coming into the barrel. This should indicate that the nozzle is far forward enough, right?

I dunno. Am I missing something really basic here?

[coach]

swap out the rubber for the madbull one that comes with the ultimate.

are you using a bearing spring guide or stock? cylinder type/barrel length?
also, not that this directly affects it but, did you mod the piston for proper engagement?

[tunabreath]

Oh, should have mentioned. I tried all combinations of the stock G&G hop up unit and madbull ultimate with the firefly, stock JG, and madbull blue buckings. All still give pretty much the same FPS.

I'm using the stock spring guide, which has a washer that is about the same thickness as a bearing.

Cylinder and barrel are stock (so presumably matched). The cylinder is a type... 2? The minimum volume one (MP5K). The barrel is about 170mm
Out of interest, I tried using a KM 590mm 6.04 TN barrel, which yields... the same FPS (315 with the VFC spring).

The Element piston already comes with the second to last tooth missing, so I didn't remove any more teeth for correcting engagement with the sorbo in there.



I'm getting a really really really consistent FPS right now too, like strings of 4 or 5 BBs at exactly the same FPS. If I had a severe air seal issue (one which would cause a 40+ FPS drop), shouldn't my FPS be fluctuating quite a bit too? Or is it consistent just because the compression is good?

[Azathoth]

You are using a sorbo with a ported cylinder so there should be a slight drop in FPS. What is in those other guns that you are using as a benchmark? if they are not running sorbo or have differently ported cylinders then that can be your issue.

Take 1 BB and feed manually into the hopup unit, take the nozzle and insert it into the hopup unit, now shake the hopup unit. If you hear a ratting sound then the nozzle is not properly seating the BB. If this happens then the you can do the linked mod or sand the inside of the gearbox shell.

I have found that some tappet plates have different thickness and over time they can wear down so the mod can be really hit or miss.

Lastly, are you sure your compression is good?

You have my number call me if you need parts or more ideas

[tunabreath]

Ok, so I've swapped some bits around again.

I noticed the front end of the stock mechbox starting to crack, so everything has been moved into an Element 9mm bearing mechbox.

I've also put in an unported cylinder (TM AUG).
Using the stock barrel and the Madbull ultimate hop up/firefly bucking, I'm still getting around 330 fps from the SP120+. Using a stock G&P M16VN barrel and hop, as well as that barrel and the madbull hop/firefly bucking, I'm getting the expected 400 fps.

What combination of cylinder and barrel can I use to get higher fps from a short (sub-400mm) barrel? How much would a short tightbore improve the fps?

[Styrak]

With an M4 length barrel you should be using a ported cylinder (port closest to the rear, there are....3 types I believe.)

[tunabreath]

It's still bugging me that I've lost 30 fps compared to stock using the same cylinder and barrel, and supposedly better air seal components and a stronger spring...

I know for sure that I'm not getting any air leak issues with the hop up since the Madbull ultimate is giving me expected performance when I use the 510mm barrel. How is it that the stock G&G hits 360 fps and I can only get 330?

[The Chad]

It's like a dell.....they hate being upgraded XD

[Styrak]

Originally Posted by tunabreath

It's still bugging me that I've lost 30 fps compared to stock using the same cylinder and barrel, and supposedly better air seal components and a stronger spring...

I know for sure that I'm not getting any air leak issues with the hop up since the Madbull ultimate is giving me expected performance when I use the 510mm barrel. How is it that the stock G&G hits 360 fps and I can only get 330?

If you're using a non-ported cylinder, and you're getting expected FPS with a 510mm barrel, then of course you'll lose some FPS going to a shorter barrel.

You don't have the correct cylinder for a short barrel.

[tunabreath]

Well no, I mean, I'm getting 30 fps lower with any of the cylinders that I use compared to stock (unported AUG, ported M4/MP5, ported MP5K/stock CQD)

The ONLY setup that gives me the expected fps is the 510mm barrel and unported cylinder. The stock cylinder and stock barrel SHOULD give me more than 360 fps, but instead I get 330.

[cjboi]

I think its the hop up system, sometimes these hop up system don't align well with the barrel and the nozzle. Its kinda tight when it hits the rubber bucking that's why you're loosing alot of FPS. That happened to me when I installed a new hop up system on my p90 and my friend installed a new hop up system on his G&G m4. I mean your soft bucking should be fine. Try aligning it well and make sure the nozzle doesn't hit a snag onto the bucking. Madbull hop up unit doesn't work well on G&G m4's. I agree with styrak, don't use a ported cylinder on a short barrel.

[HKGhost]

You should really match your barrel to your cylinder. Your gun will perform better and you're not losing any fps. I suggest putting all the stock parts in and only change the spring. See if you're losing and fps then. Keep narrowing it down piece by piece until you know what you did wrong.

[tunabreath]

@cjboi
The stock hop up, the G&P test hop up, and the Madbull hop up all give 330 fps with the stock barrel and 400 fps with the 510mm barrel. I don't think the hop up is the problem, since all three of them give similar results. (although they could all be leaking the same way, but I don't think I'm doing an equally bad job of installation in all 6 tested cases - I only failed to install the bucking properly once [I thought it was on all the way and it wasn't] and this cause immediate jams and was pretty quickly realized and remedied)

@HKGhost
Small problem in that the original parts were stripped/destroyed (hence the replacement). I rather regretfully installed some questionable parts (Prometheus piston head, actually) which failed quickly and took the stock piston with it. The stock piston/piston head required modification to get the new stuff in, so I don't think I can put it back. Also, the stock G&G piston head had TERRIBLE compression in the cylinder.


Nevermind the mystery fps loss, I'm starting to question whether the goal here is even possible. Has anyone put together an AEG with an MP5K length barrel that shot 400+ fps? Or is the barrel length a hard limitation here?

[Styrak]

Barrel length is not a limitation at all.
You just need the correctly ported cylinder.