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Extremely low FPS
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Infa
Sergeant
Join Date:
Jun 2011
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#1
Extremely low FPS
6 November, 2016, 22:44
Hello there,
I am having issues with 2 guns. 1 is fully custom build and the other is standard with internal upgrade.
Both seem to suffer from the same issue (extremely low fps).
1st gun. SR25
So the parts i have are:
Retro Arms SR25 Gearbox
Retro Arms Hop up
SHS air nozzle (o ring)
SHS Cylinder type 0 ofc
SHS Cylinder Head (double o ring)
SHS Piston 19 teeth.
SHS M140 or M150 Spring (not sure as i do not remember)
Tight bore barrel 509mm 6.03 Prometheus
On chrono (Element E1000) I am getting about 140 FPS (sometimes as low as 70).
2nd Gun M4
Standard G&P Gearbox
SHS Ported Cylinder (type 2)
SHS Piston Head
SHS Air Nozle (o ring)
SHS Cylinder Head (double o ring)
Standard Hop up
M100 Guarder Spring
Tight bore barrel 363mm 6.03 MadBull
On chono (Element E1000) I am getting about 120-140 fps.
Both guns have great compression (When manually pushing Piston in the cylinder and when blocking the air nozzle so air does not escape its pretty impossible to push piston towards the end - so the compression in here is pretty good). I have tested barrel + hop up in other guns (which chorno ok) to see if this is a problem with hop-up but again the FPS was fine (so its not a problem with hop up). I have run out of ideas of what what cause this issue.
I mean where the hell the air is going or what else is going on ? Any idea how to diagnose this or where the problem is (if someone experienced similar issue?)
Thanks
Sprint
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#2
6 November, 2016, 22:52
Re: Extremely low FPS
From what youve said, air nozzle to bucking lips?
Could be the nozzle / hop unit / bucking combo, or a tappet plate issue (gun firing when nozzle isnt fully forward / home)
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Ells
Lieutenant Colonel
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#3
7 November, 2016, 01:06
Re: Extremely low FPS
You 100% sure you have the correct nozzle length, shs sell quite a few different nozzles for the same models.
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Sitting Duck
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#4
7 November, 2016, 11:40
Re: Extremely low FPS
SR25 should be using the SHS AR10 nozzle 24mm aprox not usual m4 21.5mm nozzle
as been said nozzle not sealing on lips, could shave front of tappet plate but that is quite a drop on both guns
the G&P one should be about right or a little low but that drop is quite a bit tbh
has the gearbox's been tightened when fitting and now pointing upwards at front ?
this can cause the nozzle to scrape on hop unit and impede the nozzle moving fully forward to seal 100%
sounds like at least one or both are suffering this possible problem if correct nozzle is fitted
for $hits n giggles, remove upper receiver, load bb into hop unit, hold hop against lower box
(3 hands may be required)
test gun on chrono - this may take a few attempts but try it anyway with hop/barrel pushed against box
see what readings you are getting - should indicate that hop is not sitting nicely against box in upper receiver
should have a spring on there pushing hop against box, some use plastic/rubber to push hop firmly against box
no spring or very weak spring will allow it to blow out and lose fps
your mag(s) could be trying to pull the hop away from hop unit and poor seal = drop in fps
but those readings - especially the SR25 with m140/150 spring is bloomin' dire when you should be @ 450-500fps
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Sprint
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#5
7 November, 2016, 11:48
Re: Extremely low FPS
Originally posted by
Sitting Duck
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your mag(s) could be trying to pull the hop away from hop unit and poor seal = drop in fps
Had this on my ICS 552 when using MAG midcaps
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sparrowhawk
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#6
7 November, 2016, 13:11
Re: Extremely low FPS
Turn over gun use without a mag,put a small piece of tissue paper where the bb would enter from mag and fire the gun,if you have a poor hop air nozzle seal the tissue will fly off the air nozzle
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Infa
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#7
13 November, 2016, 23:54
Re: Extremely low FPS
Did the trick with tissue and the tissue barely moved on both guns. Both guns have correct nozzle lengths 24mm for SR25 and M4 has 21.4mm. I have Amoeba Mags for M4 and G&G for SR25 and they seem to sit pretty well in the receivers. Also I am using orings to push the barrel towards the box - so there is little to now movement what so ever.
I tried holding the barrel against the gearbox with Mag inserted but this was not really working as i could not get any reliable reading on chrono. Also i have checked (while nozzle in fully forward position) whether its touching hop up bucking (as i can see bucking while looking down the hop-bb entry) and it seemed like the nozzle is fully touching the bucking.
@Sprint, how would i diagnose/repair the tapped issue ?
Thanks
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Sprint
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#8
14 November, 2016, 08:59
Re: Extremely low FPS
Hi Infa, i thought you had it sorted, what a pain!
The tappet issue has the same effect as a nozzle thats to short, IE it wouldnt allow the nozzle to seat into the bucking.
If you have the correct nozzle, you can verify that ther nozzle penetrates the bucking lips and you have passed the tissue paper test then you do not have a problem with your tappet plate.
To be losing that amount of FPS there is something big and simple at fault, i would also expect it to be very noisy, either from air escaping or the piston slamming into the cylinder head.
With the gbox removed, lightly place your finger over the nozzle to block it (obviously you need the nozzle to have freedom of movement while the mech cycles so dont push too hard) and fire on semi, you should be able to visible see the piston stall early in its travel down the cylinder, indicating excellent air seal.
Youll only be able to test this on your M4 i would have thought as the SR25 wont have any ports on the cylinder to look through.
If you have great nozzle / hop bucking seal then only other cause it that you are not generating any pressure.
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Infa
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#9
20 November, 2016, 17:21
Re: Extremely low FPS
Hey Sprint,
Nah did not had time to look at it - I do generate pressure as i can feel air at the nozzle and barrel end. I will probably look at the guns more thoroughly over this week. I do have this weird idea that perhaps the body it self is at fault. All the components work when tested in another gun, but when i assemble the gun in original body things start to get awkward. Maybe the body is somehow miss-aligning the whole GB/Hop ?
Will test and see, anyway thanks for the input to everyone so far
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Sprint
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#10
20 November, 2016, 18:20
Re: Extremely low FPS
Sparrowhawks tissue test proves that your nozzle is aligned and penetrating the bucking, creating an air seal.
You must surely not be generating any pressure, just volume/flow.
Is it noisy in operation?
Either way, i want to know what the problem(s) are when you fix it :P
If you have either gun complete in standard parts, swap out chunks at a time, see what changes
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