Strange S400 Chrony results left me baffled

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Snesy
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Joined: Mon Aug 27, 2018 6:52 pm

Strange S400 Chrony results left me baffled

Mon Aug 27, 2018 8:10 pm

Hi all, my first post here so please bear with me..

So I decided to do a full chrony on my s400 superlite from a full tank of 190 all the way down to 100 bar so I could get a much better understanding of where exactly my sweet spot starts and ends rather then just going with the obligatory fill to 160 ish and off you go. But my results have left me wondering that something might be wrong with my rifle...

My First results : https://drive.google.com/file/d/0B5WVhD ... sp=sharing

So this was 150 shots from a full charge down to just under 100 bar... now to my understanding an unregulated rifle should have a rough power curve kinda like a rainbow... right?? So why dose mine just keep slowly rising and rising before dropping right off without ever flattering out slightly??

My first guess was maybe the hammer and rail was gunged up so i strip the gun completely down to find that was indeed the case, so i polished them up and they now glide swimmingly, yay i thought that was easy, so i reassembled the gun and did Another 150 string exactly the same as before only to find that I've somehow ended up with virtually the same results as before, shown here.

Second Test results:
https://drive.google.com/file/d/0B5WVhD ... sp=sharing

I'm stumped... am i missing something?? or is this in fact how a full test should look?

Any ideas or surgestions people?

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TenMetrePeter
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Location: Luton Beds UK

Re: Strange S400 Chrony results left me baffled

Mon Aug 27, 2018 10:03 pm

Repeatably strange!
Strangely repeatable.
A pressure dependant intermittent fault and I assume about the same pressure both times.
Any faults in the hammer or trigger would surely occur randomly across the pressure range.
Has to be the firing valve??

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tonyc
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Re: Strange S400 Chrony results left me baffled

Tue Aug 28, 2018 10:24 pm

The other thing I would check is the pot.

I would expect the curve to be flatter and the starting point to be higher. The low power at the start of the cycle could explain why you are getting so many shots. When the pot fell off my S400 the peak power increased and moved to a lower pressure. The function of the pot is to restrict air flow , thereby reducing the power at lower pressures and flattening the curve. I'm thinking the power is increasing to a point where pressure is too low to close the firing valve in a consistent manner and/or possibly you are getting hammer bounce.

Have you had the gun for long? Any relevant maintenance history or modifications?

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Archer50
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Location: Perth

Re: Strange S400 Chrony results left me baffled

Wed Aug 29, 2018 5:37 pm

Ooh err :?

I agree with Tonyc. Unless the gun has been seriously modified in some way, the problem is most likely to be with the valve or pot. I've seen something like this (although not so extreme) with very low valve spring pressure. If you haven't already done so, I suggest you remove the pot, clean and degrease everything including the valve stem and the channel it runs in and reset with the pot length at the usual 57mm. Make sure the grub screw securing the pot is nipped up to stop the pot 'self-adjusting'.

Let us know what happens. You can fiddle and fine tune them 'til the cows come home (and we do!) but your problem is intriguing, as there is so little that can produce seriously odd results like this in an S-series gun unless something is actually broken.

Good luck

Alan

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Snesy
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Joined: Mon Aug 27, 2018 6:52 pm

Re: Strange S400 Chrony results left me baffled

Wed Aug 29, 2018 5:53 pm

Hi guys,

Gun history.... I’ve had the rifle from new, coming up 4 years now, when I first serviced the gun about a year ago the firing pot and grub screw had managed to work there way loose as you suggested it may have, but I reset the pot to 57.5mm I believe I did at the time.. not 100% sure tho, But still 0.5mm out wouldn’t cause this bad results.. would it? I’m not sure how long the firing pot was loose for? And It was very loose/wobbly when I came to tighten it back at the time. Maybe it being very loose for a prolonged period of time whilst being used damaged the spring and pin??? Is that possible?? How would I be able to test to see?

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Archer50
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Joined: Mon Jun 20, 2016 5:06 pm
Location: Perth

Re: Strange S400 Chrony results left me baffled

Wed Aug 29, 2018 8:19 pm

First off, 0.5 mm on the pot would make a small difference in the power curve, but strictly fine adjustment nothing like you are seeing. 57-ish is just a sensible place to start.

It should be easy enough to see whether the valve is damaged. The pin should slide in and out absolutely smoothly under its own weight and there shouldn't be any roughness or extrusion on the valve face. I can't remember what force is required to depress the valve to test the spring (someone here will probably know), but to be honest, after 4 years if I was in any doubt I would just get a new spring and valve.

Having said that, I will be a bit surprised if you don't find that the pot has separated or gone walkies again.

A

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Snesy
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Joined: Mon Aug 27, 2018 6:52 pm

Re: Strange S400 Chrony results left me baffled

Wed Aug 29, 2018 8:58 pm

Update..

Think i might have found the problem....

So i took the cylinder off tonight go have a look at the Pot which was still set at 57.5mm form when i last serviced and adjusted it. When i removed the Pot i noticed which i can only assume was an over site on my own behalf from last time i serviced and set the pot, the collar that sits inside the Pot that holds the spring one end while the other end of the spring is over the back of the Firing Pin was the other way around so the metal collar was up against the back of the firing pin which is the same diameter so its not like it even fits over it!! FFS
Dunno if that makes sense so i did a little drawing:
The bottom drawing was how it was..
The Top drawing is how it is now..

https://drive.google.com/file/d/0B5WVhD ... sp=sharing

Any who after re assembling and setting the Pot to 57mm this time, i found just dry firing sounded a lot better so i filled it to 120bar and did a quick shot in the garden over chrony which came out at 819FPS!! (looks as tho nothings hindering it now) needless to say I've fully wound in the power adjustment screw for the time being and did another shot (515FPS) to make sure I'm legal till i can get down the range on Sunday and preform another full string of shots and fine tune her in to about 770-780FPS

Hopefully it was just my own stupidity here but I'll report back either way Sunday with my results..

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Snesy
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Joined: Mon Aug 27, 2018 6:52 pm

Re: Strange S400 Chrony results left me baffled

Fri Sep 07, 2018 6:55 pm

So I managed to get down the range and Perform another set of test which ended up basically the same... First shot start around the 710fps mark and gradually rises to about 790-780 over 150 shot again. Only difference now is when it drops off around 100 bar it doesn’t spike down and up like the last previous tests it just drops off nice and gently like it should.

I did notice during testing however, that the power adjustment screw was leaking air around the threat or somewhere during every single shot I took rather then directed it all through the transfer port to the barrel, adjusting the screw all the way in or out it made no difference and would still leak.

Dose the power adjustment grub screw have an o-ring? Or dose/would of the anti tamper plug itself act as a stop?

Either way, I happened to have a longer m3 grub screw lying around so I wrapped it in PTFE and wound it very snugly into place... now no leaks upon firing! Yay problem solved.

So all in all there was a... gunged up hammer and rail, incorrectly fitted firing pin spring and a leaking power adjustment screw..

Just shows what a bit of regular maintenance could of prevented.

Thank you everyone who helped steer me in the right direction.

Happy shooting.

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tonyc
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Joined: Mon May 29, 2017 10:55 am

Re: Strange S400 Chrony results left me baffled

Fri Sep 07, 2018 8:38 pm

Something still not right. At 190 bar you should be getting at least 750fps, more likely 760fps if peak is at 780.
Just checked data for my S400f Classic .177: AADF 4.51 with peak at 780fps, getting 100shots above 760fps and 60 shots above 770.

150 shots is well above expected. So either you are putting in more air than you think or the valve is still not opening properly at higher pressures. Could just be an inaccurate pressure gauge, so if your sweet spot is similar to mine I wouldn't worry. If your curve isn't as flat perhaps you should investigate further.

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TenMetrePeter
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Location: Luton Beds UK

Re: Strange S400 Chrony results left me baffled

Fri Sep 07, 2018 10:02 pm

Snesy wrote:
Fri Sep 07, 2018 6:55 pm


I did notice during testing however, that the power adjustment screw was leaking air around the threat or somewhere during every single shot I took rather then directed it all through the transfer port to the barrel, adjusting the screw all the way in or out it made no difference and would still leak.
The adjuster only has a spot of plastic half way along it to give it friction. So it will leak a whiff if you don't replace the A/T cover with a m3x5 round head screw preferably security torx. If you leave it open not only will it leak but it makes it easily adjustable while shooting and therefore "illegal". (probably)
If you fit a security torx screw and leave the security bit at home its "more legal" than a plain screw.
(Other opinions are available.)

I'm also a little concerned that adjusting the grub screw made no difference. Screwing it out should go into FAC territory.

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