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 Post subject: Bad seal?
PostPosted: Wed Mar 27, 2019 6:22 pm 
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Joined: Mon Aug 26, 2013 12:19 pm
Posts: 82
Location: Alvinston, Ontario
How does one go about figuring if they have a bad piston seal? Low feet per sec or ES?
I have a Benjamin .22 Classic shooting at 648fps with an ES of 8fps with Crosman domed 14.3gr. With JSB Heavies 18.13gr 5.52, 566fps an ES of 4fps. Thinking I should order several different JSB weights in 5.52.

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 Post subject: Re: Bad seal?
PostPosted: Wed Mar 27, 2019 6:58 pm 
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Joined: Fri Jan 22, 2010 1:17 pm
Posts: 1749
Location: Kingston, ON
That seems about right for that platform.

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 Post subject: Re: Bad seal?
PostPosted: Wed Mar 27, 2019 7:14 pm 
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Joined: Mon Aug 26, 2013 12:19 pm
Posts: 82
Location: Alvinston, Ontario
Neighbor has same step up, averaging 717fps, spread of 25fps.
I'm also running the thrust bearings and washers in the piston. About 5.3mm of shim.

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 Post subject: Re: Bad seal?
PostPosted: Wed Mar 27, 2019 7:45 pm 
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Joined: Wed Jan 05, 2011 12:35 pm
Posts: 5882
Location: P.G. B.C.
cwild1971 wrote:
How does one go about figuring if they have a bad piston seal? Low feet per sec or ES?
I have a Benjamin .22 Classic shooting at 648fps with an ES of 8fps with Crosman domed 14.3gr. With JSB Heavies 18.13gr 5.52, 566fps an ES of 4fps. Thinking I should order several different JSB weights in 5.52.

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The spread of your gun sounds just great. If you were shooting and got a drop to 500fps with the 14.3's, you would likely need either a new spring or a new seal, or both.

Whether a damaged seal will give greater shot to shot velocities or not, I do not know. Likely only sub-standard speeds.
Variations shot to shot of 25 seems high, but the higher speed of over 700fps if same gun sounds like nothing wrong with the pistol.

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 Post subject: Re: Bad seal?
PostPosted: Wed Mar 27, 2019 8:18 pm 
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Joined: Mon Aug 26, 2013 12:19 pm
Posts: 82
Location: Alvinston, Ontario
I will leave well enough alone then and work on the crappy Crosman trigger.

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 Post subject: Re: Bad seal?
PostPosted: Mon Apr 08, 2019 6:11 pm 
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Joined: Mon Aug 26, 2013 12:19 pm
Posts: 82
Location: Alvinston, Ontario
Didn't leave well enough alone. Returned gun to stock and took back. New gun 437fps, sleeve, spring, thrust washers, 713fps, ES of 12.
Still having accuracy and crap trigger issues. Down to about 3/4" from 1 1/2-2" groups at 10yds. Time to try some different weights and diameters. Using Crosman 14.3 right now.
Thinking of JSB 13.4 thru 18.13 at 5.52.

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 Post subject: Re: Bad seal?
PostPosted: Sun Apr 14, 2019 9:33 pm 
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Joined: Sat Jan 25, 2014 9:16 pm
Posts: 1233
Location: United States
Pretty much all the oem seals are bad, which are obvious when you look at them, but they don't get worse as a general rule. Lots of things contribute to the low power, so imo you just have to open it up and go over everything. Breaking 750 w/ 14.3gr pellets is doable with all the oem parts. I have all that info, plus what is imo the ideal trigger fix if you want it


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 Post subject: Re: Bad seal?
PostPosted: Mon Apr 15, 2019 5:30 pm 
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Joined: Mon Aug 26, 2013 12:19 pm
Posts: 82
Location: Alvinston, Ontario
Actually have your tuning guide and have applied most principals. Forgot about the Crosman trigger modd you had included. Have never had a trigger as poor as a Crosman before.

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