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PostPosted: Sat Jul 25, 2020 4:01 pm 
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My non-PAL Crosman Optimus shoots anywhere from 400-450 fps through a chrony. I'm thinking that a new breech seal and shim should do the trick to make it slightly faster and to be more consistent... I know the Crosman part number is B12-00-14, but I'm thinking that a trip to Home Depot would be more efficient than paying for shipping. Does anyone have the actual dimensions of the breech seal? Or an equivalent/compatible O-ring replacement? Same with a shim washer.

Mark


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PostPosted: Sat Jul 25, 2020 4:30 pm 
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Location: Kingston, ON
Put a shim behind the existing breach seal. I have used a variety of shim materials. One thing that works well is electrical solder wire. Coil it to approx the right size and then flatten a bit with a hammer to the right thickness, make several layers if you need to. If your breach seal is visibly torn, then this may not help. Otherwise give it a go and see if your guns shoots more consistently.

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PostPosted: Sat Jul 25, 2020 4:52 pm 
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Location: Ontario, Canada
Also try flipping the seal over. I shim with several windings of dental floss. I wrap the floss around a pencil and then slide it into the groove.


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PostPosted: Sat Jul 25, 2020 4:54 pm 
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Location: Somewheres near the Atlantic
According to Chevota,
Quote:
The breech seal can be replaced with a rubber O-ring, which is better and how most all guns do it. It takes a size AS568-109 (aka -109), or plumbing size 1/2"OD x 5/16"ID x 3/32" thick, or Crosman # CRS5177A013.


I would think the plumbing section O rings would be softer, easier to tear and need to be replaced more.

Well Crosman.ca does offer flat rathe shipping at 9.95 and free after 35$.


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PostPosted: Sat Jul 25, 2020 7:25 pm 
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Location: Thunder Bay,On.
mwlcarter wrote:
My non-PAL Crosman Optimus shoots anywhere from 400-450 fps through a chrony. I'm thinking that a new breech seal and shim should do the trick to make it slightly faster and to be more consistent... I know the Crosman part number is B12-00-14, but I'm thinking that a trip to Home Depot would be more efficient than paying for shipping. Does anyone have the actual dimensions of the breech seal? Or an equivalent/compatible O-ring replacement? Same with a shim washer.

Mark



Go to any hydraulics shop in your town and ask for a Viton V75-109 o-ring...$0.56..
works great.. :D

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PostPosted: Sun Jul 26, 2020 9:49 am 
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here is the exact breech seal replacent for many of the Crosman break barrels...including yours...
the v90 also works...its a little harder seal if so desired...
https://www.globaloring.com/product/v75109/

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PostPosted: Tue Jul 28, 2020 2:42 pm 
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Thanks everyone. I tried the dental floss and flipping o Er tricks, but I actually had a reduction in fps... So I put it back to normal and it went back to 400-450. I've ordered some v75-109 orings, that should do the job.


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PostPosted: Sat Aug 08, 2020 2:27 pm 
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So, I'm getting a little confounded here... I ordered the Viton 109 o-rings to replace the breech seal in my Crosman Optimus (.177, 495 fps version). Originally I was having a fairly broad range of 400-450 fps. Every time I've replaced the breech seal and/or tried making a shim (latest shim attempts were solder hammered thin... there seems to be very little if any room for a shim without tearing the o-ring), I'm seeing a reduction in fps to 350-400 fps.

Any tips? I'm kind of hoping I'm making a common mistake. I just want to bump up my Optimus to as close to 500 fps as possible.

Incidentally, using the Viton 109 to replace the breech seal in my Xisico XS12 (.22) saw my fps go up by about 30-40 fps. Getting frustrated that I can't seem to get any consistency with the Optimus.

A thought that's occurred... if my Optimus has a bleed hole in the piston, would the bleed hole result in not only limiting the maximum pressure but also be resulting in a constant loss of air? I'm wondering if that would account for the broad variance in speeds to begin with, and prevent much consistency shot to shot.


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PostPosted: Sat Aug 08, 2020 2:36 pm 
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Joined: Mon Aug 08, 2016 7:23 am
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Location: Somewheres near the Atlantic
mwlcarter wrote:
So, I'm getting a little confounded here... I ordered the Viton 109 o-rings to replace the breech seal in my Crosman Optimus (.177, 495 fps version). Originally I was having a fairly broad range of 400-450 fps. Every time I've replaced the breech seal and/or tried making a shim (latest shim attempts were solder hammered thin... there seems to be very little if any room for a shim without tearing the o-ring), I'm seeing a reduction in fps to 350-400 fps.

Any tips? I'm kind of hoping I'm making a common mistake. I just want to bump up my Optimus to as close to 500 fps as possible.

Incidentally, using the Viton 109 to replace the breech seal in my Xisico XS12 (.22) saw my fps go up by about 30-40 fps. Getting frustrated that I can't seem to get any consistency with the Optimus.

A thought that's occurred... if my Optimus has a bleed hole in the piston, would the bleed hole result in not only limiting the maximum pressure but also be resulting in a constant loss of air? I'm wondering if that would account for the broad variance in speeds to begin with, and prevent much consistency shot to shot.


Did you remove the factory shim, and just try it with the o ring?


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PostPosted: Sat Aug 08, 2020 3:13 pm 
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There doesn't appear to be a factory shim, or if there is I don't see how to remove it.


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PostPosted: Sat Aug 08, 2020 3:19 pm 
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Location: Somewheres near the Atlantic
mwlcarter wrote:
There doesn't appear to be a factory shim, or if there is I don't see how to remove it.


EVP shows there is one. Magnet or pick.

https://support.crosman.com/hc/en-us/ar ... P___PL.pdf


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