Odd FPS from new build

m102404 · April 5th, 2009, 23:28

I built up a new mechbox for testing...and the initial results are a bit puzzling...

Base:
- Guarder Reinforced mechbox (good old tried and true)
- old gear set (previously tested)
- PP hard piston
- MASK aluminum piston head (non-ported)
- MASK aluminum cylinder head
- modify airseal nozzle (m4/m16)
- bearing spring guide
- M110 spring
- M4 cylinder
- KA Hopup
- Guarder black hopup rubber
- somebrand SIG55x length inner barrel (a bit longer than M4)
- other bits & pieces

Although I've built the odd M4 mechbox before and have fiddled with a couple of AEGs in the past

...and I'm pretty sure of what results I should get, I'm open to any and all suggestions!

With a previous mechbox in this setup, I'd get just around 400fps with this setup. Compression seems fine.

Chrony after two assemblies is a very consistent 285fps w/ 0.20g. Mechbox "sounds" good (it's actually a bit noisy with the gears, but the sound of the shot sounds like a high-300fps)

I'll check the nozzle next tear down...maybe I'll swap the inner for a stock M4 barrel (hate taking off the KA hopup c-clip).

Or...I'll just swap a different piston head/cylinder head in there and see what happens.

A bit baffled with the low FPS.

Tired, going to sleep on it.

Tys

The Saint · April 5th, 2009, 23:31

This might sound silly, but there's no chance that you got a mislabelled spring, right?

m102404 · April 5th, 2009, 23:36

LOL...it's not labeled at all...it's from my misc. bin. Feels like a M100 or M110. Certainly not a M85!

It's actually the second "M110" I tried. The original spring was a Madbull dark blue (which is a M110 I think). Thank you for mentioning it though...I had forgotten the previous spring until you asked.

Both springs "felt" the same...or very close.

coach · April 6th, 2009, 09:21

double check your BB weight.

m102404 · April 6th, 2009, 10:14

I'm 99.99% sure they're 0.20's. The only weights I have that would drop it that much are Madbull's and they're colour coded.

I chronied other repairs the same night and they chronied as expected with the same BB weight.

I've got a big bag of Madbull 0.20's that I fill my hicaps for testing/chrony-ing.

Tys

Jimski · April 6th, 2009, 10:55

nozzle-hop-up connexion that leaks ?

Crunchmeister · April 6th, 2009, 11:06

Interested in hearing the outcome of this. Having a similar issue with the custom mechbox I built for my HK416. It's only got an MS90SP spring (set up for indoors). It sounds powerful. Air seal seems good and the air coming out of the nozzle when the box is fired seems very comparable to my custom C8 that's also loaded with an identical spring and chronies about 325 with .2. But the 416 seems to chrony about 240-245 instead... It's a very consistent velocity, but about 50 fps too low...

CDN_Stalker · April 6th, 2009, 11:40

Quote:

Originally Posted by Jimski

nozzle-hop-up connexion that leaks ?

Saggy diaper that leaks? Lol

Anyways, this is something I've found before too, way too often. Airleaks drive me nuts to troubleshoot!

Flatlander · April 6th, 2009, 12:10

Have you tried the flashlight in the hopup while looking down the barrel trick so see if the nozzle is sealing on the rubber?

I've got a similar issue with my SPR but haven't had time to completely fix the problem yet due to school. I've got it narrowed down to an alignment problem of sorts. The nozzle isn't always sealing with the hopup rubber - I can distinctly hear when it is (gives a nice low thud sound) and when it's not it has a high pitched snap.

Anyways, as buddy found that his modify gear axles were thicker than the stock ones so his tappet plate sat further back than it was supposed to - therefore the nozzle could not travel forwards enough to seal with the rubber. He filed down the tappet plate fin slightly to compensate for the larger axle shafts.

Hope that helps. Good luck, Tys.

m102404 · April 6th, 2009, 12:28

After thinking about this a bit...I'll try the following:

Rebuild 1:
1a - swap different hopup unit/inner barrel/hopup rubber into this build
2a - swap a different M4 nozzle into this build

if that doesn't work (if it doesn't work, ideally it'll give me the same low FPS and not something almost there!)...

Rebuild 2:
- swap in different piston head/cylinder head into questionable mechbox
I can't think of why it would make such a huge difference...but it's worth trying

Last ditch
- swap in different mechbox/hopup (known good build)
maybe there's an issue with this M4 body...(hope not, it's pretty)

If none of that works...my junker bin is going to be overflowing with a box full of primo stuff and I'm switching to AK's

Splashx · April 6th, 2009, 13:41

try swaping to another tappet plate, I tryed a King arms tappet plate in my Jing gong shell and I got 250fps, Jing gong stock tappet plate without touching anything else = 370fps

so you may stick with the same brand of tappet plate and shell

Crunchmeister · April 6th, 2009, 13:50

Quote:

Originally Posted by Splashx

try swaping to another tappet plate, I tryed a King arms tappet plate in my Jing gong shell and I got 250fps, Jing gong stock tappet plate without touching anything else = 370fps

I may try this in mine. I have the stock JG tappet plate. The one I have in there now I THINK is a Modify... I may reinstall the stock JG nozzle too just to see if that helps.

Donster · April 6th, 2009, 14:03

this is what tirador told me to do. you are supposed to remove some of the teeth from the piston. the last two to be exact. he said you are only supposed to do this if you install his new cylinder head w/ sorbo (so my M14 is safe

) i dunno if that would give the results you are talking about, but im sure you can make more sense of it then i did. i am trying to upload the pic he sent me, but so far, no luck

m102404 · April 6th, 2009, 14:30

The piston teeth have been shaved (removed one and slightly shaved the next one). The sector gear clears the piston rack and engages nicely.

I'll have to check what tappet is in there now...can't recall. I'll check it out and consider swapping it as part of the first rebuild.

Thanks!

Tys

m102404 · April 7th, 2009, 00:27

weird...just plain weird...

Rebuilt the mechbox...new piston, piston head, cylinder head, nozzle...400fps spring, Guarder black hopup rubber/nub, KA hopup unit, different M4 inner...best it'll do is a meager 330fps...

I swapped a complete new upper onto it...systema hopup, 6.01mm 300mm short inner...shot 330-ish...

Tried my upper on another lower (that should shoot 350)...and it shot just under 340fps....

Confused...but resisted the urge to chuck it against the wall...so at least the evening ended ok...

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April 5th, 2009, 23:28	#1
m102404 Tys Trader rating Join Date: Apr 2006 Location: Toronto	Odd FPS from new build I built up a new mechbox for testing...and the initial results are a bit puzzling... Base: - Guarder Reinforced mechbox (good old tried and true) - old gear set (previously tested) - PP hard piston - MASK aluminum piston head (non-ported) - MASK aluminum cylinder head - modify airseal nozzle (m4/m16) - bearing spring guide - M110 spring - M4 cylinder - KA Hopup - Guarder black hopup rubber - somebrand SIG55x length inner barrel (a bit longer than M4) - other bits & pieces Although I've built the odd M4 mechbox before and have fiddled with a couple of AEGs in the past ...and I'm pretty sure of what results I should get, I'm open to any and all suggestions! With a previous mechbox in this setup, I'd get just around 400fps with this setup. Compression seems fine. Chrony after two assemblies is a very consistent 285fps w/ 0.20g. Mechbox "sounds" good (it's actually a bit noisy with the gears, but the sound of the shot sounds like a high-300fps) I'll check the nozzle next tear down...maybe I'll swap the inner for a stock M4 barrel (hate taking off the KA hopup c-clip). Or...I'll just swap a different piston head/cylinder head in there and see what happens. A bit baffled with the low FPS. Tired, going to sleep on it. Tys

April 5th, 2009, 23:31	#2
The Saint Trader rating Join Date: Jan 2005 Location: Quebec	This might sound silly, but there's no chance that you got a mislabelled spring, right? __________________ "The Bird of Hermes is My Name, Eating My Wings to Make Me Tame."

April 6th, 2009, 10:55	#6
Jimski Trader rating Join Date: Jun 2005 Location: Montreal	nozzle-hop-up connexion that leaks ? __________________

April 5th, 2009, 23:36	#3
m102404 Tys Trader rating Join Date: Apr 2006 Location: Toronto	LOL...it's not labeled at all...it's from my misc. bin. Feels like a M100 or M110. Certainly not a M85! It's actually the second "M110" I tried. The original spring was a Madbull dark blue (which is a M110 I think). Thank you for mentioning it though...I had forgotten the previous spring until you asked. Both springs "felt" the same...or very close.

April 6th, 2009, 09:21	#4
coach aka coachster Trader rating Join Date: Mar 2008 Location: T dot	double check your BB weight.

April 6th, 2009, 10:14	#5
m102404 Tys Trader rating Join Date: Apr 2006 Location: Toronto	I'm 99.99% sure they're 0.20's. The only weights I have that would drop it that much are Madbull's and they're colour coded. I chronied other repairs the same night and they chronied as expected with the same BB weight. I've got a big bag of Madbull 0.20's that I fill my hicaps for testing/chrony-ing. Tys

April 6th, 2009, 11:06	#7
Crunchmeister Trader rating Join Date: Nov 2007 Location: In your bedroom going though your underwear drawer	Interested in hearing the outcome of this. Having a similar issue with the custom mechbox I built for my HK416. It's only got an MS90SP spring (set up for indoors). It sounds powerful. Air seal seems good and the air coming out of the nozzle when the box is fired seems very comparable to my custom C8 that's also loaded with an identical spring and chronies about 325 with .2. But the 416 seems to chrony about 240-245 instead... It's a very consistent velocity, but about 50 fps too low... __________________

April 6th, 2009, 12:10	#9
Flatlander Trader rating Join Date: Mar 2007 Location: Edmonton	Have you tried the flashlight in the hopup while looking down the barrel trick so see if the nozzle is sealing on the rubber? I've got a similar issue with my SPR but haven't had time to completely fix the problem yet due to school. I've got it narrowed down to an alignment problem of sorts. The nozzle isn't always sealing with the hopup rubber - I can distinctly hear when it is (gives a nice low thud sound) and when it's not it has a high pitched snap. Anyways, as buddy found that his modify gear axles were thicker than the stock ones so his tappet plate sat further back than it was supposed to - therefore the nozzle could not travel forwards enough to seal with the rubber. He filed down the tappet plate fin slightly to compensate for the larger axle shafts. Hope that helps. Good luck, Tys. __________________ Ronin 49 Team Member

April 6th, 2009, 12:28	#10
m102404 Tys Trader rating Join Date: Apr 2006 Location: Toronto	After thinking about this a bit...I'll try the following: Rebuild 1: 1a - swap different hopup unit/inner barrel/hopup rubber into this build 2a - swap a different M4 nozzle into this build if that doesn't work (if it doesn't work, ideally it'll give me the same low FPS and not something almost there!)... Rebuild 2: - swap in different piston head/cylinder head into questionable mechbox I can't think of why it would make such a huge difference...but it's worth trying Last ditch - swap in different mechbox/hopup (known good build) maybe there's an issue with this M4 body...(hope not, it's pretty) If none of that works...my junker bin is going to be overflowing with a box full of primo stuff and I'm switching to AK's

April 6th, 2009, 13:41	#11
Splashx Trader rating Join Date: May 2007 Location: Near Quebec city	try swaping to another tappet plate, I tryed a King arms tappet plate in my Jing gong shell and I got 250fps, Jing gong stock tappet plate without touching anything else = 370fps so you may stick with the same brand of tappet plate and shell Last edited by Splashx; April 6th, 2009 at 13:46..

April 6th, 2009, 14:03	#13
Donster Trader rating Join Date: Jul 2007 Location: GTA	this is what tirador told me to do. you are supposed to remove some of the teeth from the piston. the last two to be exact. he said you are only supposed to do this if you install his new cylinder head w/ sorbo (so my M14 is safe ) i dunno if that would give the results you are talking about, but im sure you can make more sense of it then i did. i am trying to upload the pic he sent me, but so far, no luck

April 6th, 2009, 14:30	#14
m102404 Tys Trader rating Join Date: Apr 2006 Location: Toronto	The piston teeth have been shaved (removed one and slightly shaved the next one). The sector gear clears the piston rack and engages nicely. I'll have to check what tappet is in there now...can't recall. I'll check it out and consider swapping it as part of the first rebuild. Thanks! Tys

April 7th, 2009, 00:27	#15
m102404 Tys Trader rating Join Date: Apr 2006 Location: Toronto	weird...just plain weird... Rebuilt the mechbox...new piston, piston head, cylinder head, nozzle...400fps spring, Guarder black hopup rubber/nub, KA hopup unit, different M4 inner...best it'll do is a meager 330fps... I swapped a complete new upper onto it...systema hopup, 6.01mm 300mm short inner...shot 330-ish... Tried my upper on another lower (that should shoot 350)...and it shot just under 340fps.... Confused...but resisted the urge to chuck it against the wall...so at least the evening ended ok...

Odd FPS from new build

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