Low fps could it be cylinder related?

[Pollynator_bravo2]

I’ve found a home for a gear box I had to take out of a polycarb body that broke. It’s got a M105 spring, eon piston head, cylinder head etc. The inner barrel on the previous gun was was under 300mm and I’d get a good 300fps on 0.25g. This guns inner barrel is over 300mm and I’m getting 215fps on 0.25g ?

Ive checked the compression on the cylinder and nozzle and piston and it’s spot on. 
is it possible the cylinder port needs to be further back so I need to buy another one? 
 

or could it be something else ?

 

[Lozart]

Picture of the cylinder?

Where is the vent on the cylinder? 

 

[Pollynator_bravo2]

View attachment 134212
useless picture I know but the only one I have currently. I think it’s about half way down to two thirds of the way

 

[Colin Allen]

View attachment 134212
useless picture I know but the only one I have currently. I think it’s about half way down to two thirds of the way

That looks like the standard G&G cylinder; what is the inner barrel length?

 

[Pollynator_bravo2]

I’ll measure up and check 

 

[Lozart]

Pending further info, it could be under volume for the barrel length but it may just be fitment with the rest of the gun.

 

[Pollynator_bravo2]

This is the cylinder. I managed to find the invoice from when I brought it. I’m taking the gun apart this avo so I’ll measure the inner barrel

View attachment 134225

 

[Rogerborg]

I'd suspect the nozzle-to-hop rubber seal.  All we know so far is that it's (probably) a V2 box, we don't know the nozzle length, the hop unit, or the rubber that you're using.  Maple Leafs have longer lips than some other rubbers, that might help, or you might need a longer nozzle, or it might very well be something entirely different. Airsoft, innit.

 

[Skara]

Plenty of threads already on sorting out the power and various issues.

It could be the cylinder (doubt it, that thing should be good up to 360mm barrels), it could be the nozzle timing, nozzle length, nozzle air seal, hop unit fitment, hop rubber lips, general compatibility between these parts. Could be the tappet plate, delayer chip, tappet plate spring, tappet plate compatibility with the gearbox shell, number of teeth removed off the sector gear.....

All the info we have is the cylinder size and barrel length..

I reckon it's time to write an article on the matter and then copypasta it everywhere....

 

[Pollynator_bravo2]

So it’s a V2 gear box, Maple leaf 60 degree bucking, no delay chip, 13:1 gears, 18000 ASG motor, Rocket v2 tappet plate, SHS nozzle 21.4mm, Gate EON protector cylinder head, EON Power hybrid cylinder head.
 

Hop unit looks like a basic rotary unit but it was what come with the shell/receiver when I brought it second hand. The hop unit I used to run when fitted to the inner barrel, wouldn’t let the upper receiver fit all the way into the lower Reciever (this one has happened to me twice now so I’m wondering if some how I’ve made a school boy error when putting the upper back together) 

I’ll get the measurements on the inner barrel and some more pictures later 

View attachment 134237

 

[Colin Allen]

This is the cylinder. I managed to find the invoice from when I brought it. I’m taking the gun apart this avo so I’ll measure the inner barrel

View attachment 134225

That should be ok for most M4 type barrel lengths.  I use a similar one with a 360mm barrel.

 

[Pollynator_bravo2]

That should be ok for most M4 type barrel lengths.  I use a similar one with a 360mm barrel.

Tbf I don’t think it’s over 400mm however I’ll check once I’m back home. Based on my poorly calibrated eyes I’m guessing between 350 to 370

in the past I’ve had similar platforms with nozzle related issues but I fitted an O ring to make sure the hop was as tight as poss to the gb/nozzle and the fps dropped 5 points ??‍

 

[Colin Allen]

Tbf I don’t think it’s over 400mm however I’ll check once I’m back home. Based on my poorly calibrated eyes I’m guessing between 350 to 370

in the past I’ve had similar platforms with nozzle related issues but I fitted an O ring to make sure the hop was as tight as poss to the gb/nozzle and the fps dropped 5 points ??‍

Possibly a marginally different nozzle length, a different profile, or slightly too tight on the cylinder head tube.

 

[ak2m4]

I reckon it's time to write an article on the matter and then copypasta it everywhere....

mmmmmmmm copypasta

 

[Pollynator_bravo2]

Possibly a marginally different nozzle length, a different profile, or slightly too tight on the cylinder head tube.

Probably length as it’s the same I used previously with a health fps. Maybe too short? What other lengths are there for an m4 v2gb?

 

[Colin Allen]

Probably length as it’s the same I used previously with a health fps. Maybe too short? What other lengths are there for an m4 v2gb?

I have seen 21mm and 21.4mm.  However, not all 21.4mm ones are the same length; there are marginal, but potentially significant, differences.

However, it could be a timing issue or one of many other issues which can occur when you bring different parts together.

 

[Skara]

The SHS nozzles I bought a while ago were supposed to be 21.3 but they turned out to be 21.5 and change..

Length also depends on the hop unit, hop rubber and inner barrel, some combinations love short nozzles, others want longer.

For example the Maxx TE hop I have in my pdw says it wants 21.25mm tops but ran fine on the aforementioned 21.5mm shs nozzle for a while.

 

[Colin Allen]

The SHS nozzles I bought a while ago were supposed to be 21.3 but they turned out to be 21.5 and change..

Length also depends on the hop unit, hop rubber and inner barrel, some combinations love short nozzles, others want longer.

For example the Maxx TE hop I have in my pdw says it wants 21.25mm tops but ran fine on the aforementioned 21.5mm shs nozzle for a while.

Indeed.  There is no consistency in airsoft and tolerances are loose.

 

[Dan Robinson]

Indeed.  There is no consistency in airsoft and tolerances are loose.

And yet microns mean the difference between our toys working or not.....expensive or not *sigh*

 

[Pollynator_bravo2]

I have seen 21mm and 21.4mm.  However, not all 21.4mm ones are the same length; there are marginal, but potentially significant, differences.

However, it could be a timing issue or one of many other issues which can occur when you bring different parts together.

When you say timing do you mean when the nozzle moves forward and locates the bb into the feed lips before the piston sends the air down? Sorry if that’s a stupid question 

also where should the nozzle

locate to when it enters the hop again?

I am not getting any miss feeding when the gun fires bbs fly so I think the retraction etc is ok