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PostPosted: Sat Feb 01, 2020 1:56 pm 
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Joined: Sat Apr 21, 2012 1:30 pm
Posts: 7
Location: Niagara Region
Hi All. Looking for suggestions from someone with lots of PCP experience.I'd be very grateful.
Bought the gun used. It's in excellent condition and I don't think it had been apart before me as it was hard to get apart the first time.
i'm well aware of the power curve and sweet spot. But it’s not shooting right.
There is no power “curve” or “sweet spot”. It's a steady downhill slope. On a fill from 190-200 bar it will start out around 995fps and continually declines to about 870fps at 110 bar (on medium setting). I tried all five power levels. Also tried 8.4’s and 10.3’s. same thing happens.
I’ve re-sealed the gun, changed the valve (rod) and the hammer spring. Have read everything possible online and can’t seem to find anything like this.
There’s no way I could use it for FT when there’s at least 50-60fps drop on 30 shots. I know they shoot better than this.
It also seems to have too much power. It’s supposed to be 20fp max. But on a fresh fill on high power it’s around 25fp.
I’m stumped. Any ideas? Only thing left I can think of is possibly the valve spring or valve body. But I don't want to keep randomly changing parts.
The good thing is I can take apart an S400 with my eyes closed now. Lol
Thank you for any help
Larry


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PostPosted: Sat Feb 01, 2020 2:20 pm 
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Joined: Wed Jan 05, 2011 12:35 pm
Posts: 6324
Location: P.G. B.C.
It sounds as if the hammer spring is too heavy, but you've adjusted/changed that so :?:

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Daryl


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PostPosted: Sat Feb 01, 2020 3:10 pm 
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Joined: Sat Mar 30, 2013 5:52 pm
Posts: 51
Location: Edmonton
Not an expert but my s410 valve spring tension can be adjusted by turning in or out the "pot", if turned out - less tension, velocity result is same with your experience. Worth a try.


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PostPosted: Sat Feb 01, 2020 5:17 pm 
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Joined: Fri Aug 24, 2007 9:21 pm
Posts: 2172
Location: Greater Napanee, ON, Canada
Is there a small opening with a set screw in it on the right side of the action block that seems to go in at a downward angle? It should be just in front of the opening where you insert the pellet. If so, the screw is a restrictor for the amount of air getting through to the valve. Screw it in for less power by restricting flow and out for more air.

Failing that, you could invest in a regulator as well. If it has a reg, it isn't working. A number of years back, Walter made me a reg for a 410 and the results were awesome. Less than 10 fps over entire fill.

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PostPosted: Sat Feb 01, 2020 7:57 pm 
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Joined: Sat Apr 21, 2012 1:30 pm
Posts: 7
Location: Niagara Region
Thanks guys

Err; This one doesn't have the screw in pot. It's one that pushes in and held in place with a small set screw.

Hi Tim. doesn't appear to have that screw. My MPR FT has the secret screw, but nothing like that on this one. I actually have a regulator. I initially installed that when I did the re-seal but it was doing strange things with that as well. So I took it out and figured I'd try to get it shooting properly, then maybe try the regulator..

:rolleyes:


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PostPosted: Sat Feb 01, 2020 8:09 pm 
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Joined: Fri Oct 20, 2017 8:29 pm
Posts: 370
Location: Southern Gulf Islands, Beautiful British Columbia, Canada
Hello LarryC,

Here's an interesting article on power curves of unregulated airguns: https://www.pyramydair.com/blog/2008/12 ... -of-a-pcp/

If your 400 is anything like my 510, you should have no more than a 15 to 18 fps spread over 40 shots. Wondering if there is a problem with the valve seal and/or associated valve spring. Adjusting or replacing the hammer spring with something lighter will reduce power but may not solve the steady declining power curve issue. A regulator will certainly help, but might not improve the excessive fps spread if the problem originates within the valve. Have you disassembled and inspected it? I'm assuming as well your rifle is .177?

Cheers!

Avianmanor

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PostPosted: Sun Feb 02, 2020 12:37 am 
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Joined: Sat Feb 28, 2009 12:28 pm
Posts: 673
Try cutting 1 coil off the spring you removed,that should start a curve,keep your fill at 200 bar,kelly


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PostPosted: Sun Feb 02, 2020 4:25 pm 
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Joined: Sat Apr 21, 2012 1:30 pm
Posts: 7
Location: Niagara Region
Thanks a lot for the ideas and replies guys. I will definitely have a better look and the valve spring, Pot and maybe clip the hammer spring..
Thanks again :)
Larry


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