Extremely LOW FPS

[turok_t]

Hey guys, so after chronoing my M4 today at Velocity Arms (Karnage is a damn nice guy btw), i found out that my highly upgraded parts give out a very shitting FPS..

Here is what Im using:

Prometheus MS120 spring
Prometheus Type C Cylinder
Prometheus cylinder head
Prometheus piston
Prometheus piston head
Prometheus air nozzle
Prometheus Neo chamber
Prometheus soft rubber
Prometheus 363mm inner barrel
SCS nub

My FPS using 0.25g bastards and G&P 9.6V battery are:

324fps
322fps
321.2fps
310fps
326.5fps

I tried to put an Element MS135 and i got around 348-360fps, but it should be MUCH higher around 410fps

So i opened up my gearbox with Frank and he tested my compression units and it was perfect. I plugged the airnozzle with one hand, and used my other hand to force the piston in and i can feel alot of resistance.

I have a feel the problem involves the interaction between the air nozzle/hop up chamber but i dont know what it is..I think there can be a lot of air leak when the air nozzle is inside the hop up chamber.. Its been quite frustrating because after all these upgrades, i still can not achieve the FPS I wanted....

Anyways, any help would be much appreciated.

[Amos]

What way did you put the spring?

[turok_t]

Originally Posted by Amos

What way did you put the spring?

I put the tight coiled end at the back part of the gearbox where the spring guide is... I did that for both the MS120 and MS135

[cjboi]

hmmm you might be right with your guess. Most of the time when the nozzle don't work well with the chamber, then most likely its your chamber. It's weird though I didn't expect that to be that low since you have the superior parts.

[Styrak]

So you're shooting about 350-360 on 0.20's with an M120. Not a "shitting FPS" but yes it's lower than it should be.

You said you checked the compression so it's likely the nozzle/hopup rubber interaction.

[HKGhost]

if the problem is where the hop up chamber meets the nozzle, try doing the tappet plate mod (I made a thread with this mod). your nozzle might be a hair too short and not making a tight seal.

[Amos]

He's using a 363mm ported cylinder with a full size 469 barrel

[turok_t]

Originally Posted by Amos

He's using a 363mm ported cylinder with a full size 469 barrel

After discussing with Riley, ive decided to get a PRom Type A cylinder and doing the tappet plate mod as well.. im gonna be getting a chrono too shortly so ill see if my FPS increases.

[yuhaoyang]

why would you get a type A...
you would just be creating the same problem, except in reverse.
Having air loss because the barrel is too short instead of the cylinder being ported too much...

[Styrak]

Originally Posted by turok_t

After discussing with Riley, ive decided to get a PRom Type A cylinder and doing the tappet plate mod as well.. im gonna be getting a chrono too shortly so ill see if my FPS increases.

Yes, the correct cylinder helps.
You should really research BEFORE you buy parts and install them, then you wouldn't have these problems.

[Crowin]

If you put in a new hop-up rubber, A harder rubber might press Too hardly on the BB. giving you a lower fps, does your fps go up or down when you increase the hopup?

[OMGWTF]

Originally Posted by Styrak

Yes, the correct cylinder helps.
You should really research BEFORE you buy parts and install them, then you wouldn't have these problems.

Nothing worse than "Shotgun" troubleshooting.. (i.e Throwing parts at it)
Take your time and do the research.

[Jackarutu]

First turok_t says: “My FPS using 0.25g bastards and G&P 9.6V battery are:”

Then Styrak : “So you're shooting about 350-360 on 0.20's with an M120. Not a "shitting FPS" but yes it's lower than it should be.”

I believe all experienced players and techs will agree that the standard is based on .20 BB’s with hop-up off. Reporting a secondary BB size might be an interesting antidote but it doesn’t really help much to make a comparison to the standard.

When I think there could be a problem with the air seal between the air nozzle and the hop-up rubber I remove the upper receiver and take out the inner barrel and get second pair of hands to hold the hop-up firmly against the gear box and in perfect alignment to the gear box: with the hop-up upside down. Then someone feeds a single BB into the hop-up and we fire thru the chrono. What this does is remove any miss-alignment between the hop-up and gear box that may be present due to fitment in the outer barrel.

If still no joy, then check the hop-up and the position of the rubber in the hop-up. This may be hard to do. The air nozzle needs to make a hard seal against the hop-up rubber.

From empirical experience working with Madbull hop-ups: I find if one gets in a hurry and doesn’t check it is very easy to get a maul formed hop-up rubber at the front of the hop-up when the air nozzle engages. When you look down the barrel from the hop-up end you should see a perfect circle. If you see a distortion in the circle pull the inner barrel back and try re-seating it again.

Hop-up rubbers can get into some really crazy problems. Just recently I got an M249 in with a fails to shoot complaint. Turns out the hop-up rubber had somehow gotten totally pushed inside the inner barrel.

I’m not trashing Madbull hop-ups. I use them on all custom jobs. Once the hop-up rubber is seated correctly they are outstanding hop-ups.

[Amos]

Originally Posted by yuhaoyang

why would you get a type A...
you would just be creating the same problem, except in reverse.
Having air loss because the barrel is too short instead of the cylinder being ported too much...

Type A cylinder because he's using a 469mm barrel.

When you're going to have the wrong cylinder (two uppers, one gearbox) it's better to have TOO MUCH air than not enough.

[yuhaoyang]

in his OP he said 363.
That's a pretty big diff.

Originally Posted by turok_t

Here is what Im using:

Prometheus 363mm inner barrel