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All Springer/NP/PCP Air Gun Discussion General > Machine Shop Talk & AG Parts Machining

Barrel/Breech o-ring size and groove dimensions for .177, .22, .25, .30, .357???

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mackeral5:
If one were wanting to machine a new barrel and probe, what is the recommended size o-ring and its associated groove dimension for a barrel/breech located o-ring?

I am specifically looking for .22, which IIRC crosman uses a -009 oring for.  What groove dimensions should be machined into the chamber? 

While I was asking this question I figured this would be a good repository for other calibers.  IF you have performed these operations successfully, what dimensions/o-ring sizes did you use?

I am certain I am oversimplifying, so please do share pertinent information as well.

Thank you in advance.

nervoustrigger:
The way I approach it is to calculate for about 10% squeeze of the O-ring’s cross-section.  In the case of a -00x size (0.070” cross-section), that means 0.007” squeeze on the radius.  For a breech O-ring scenario, it’s helpful to me to think of it in terms of the bolt expanding the ID of the O-ring to put the squeeze on it. 

Back_Roads:
 Now this topic comes up, yesterday I did a similar operation, but I did get it right enough ;)

mackeral5:

--- Quote from: nervoustrigger on May 26, 2023, 03:05:55 PM ---The way I approach it is to calculate for about 10% squeeze of the O-ring’s cross-section.  In the case of a -00x size (0.070” cross-section), that means 0.007” squeeze on the radius.  For a breech O-ring scenario, it’s helpful to me to think of it in terms of the bolt expanding the ID of the O-ring to put the squeeze on it.

--- End quote ---

Thank you.

eeler1:
If you know the size of the oring, there are spec's online for groove width and depth, depending on if it is intended for static or dynamic use.  Most of the oring manufacturers will have that stuff on their websites, for example;

https://www.parker.com/content/dam/Parker-com/Literature/O-Ring-Division-Literature/O-Ring-ehandbook-pdfs/Design-chart-4-3-for-O-ring-face-seal-glands.pdf

But as to your point, yes, it would be handy to have oring sizes for the various calibers, then it would be easier to find groove specs.  Also, some are intended to go on the bolt, others go in the barrel, might be more than one size per caliber.

While we are on the subject of orings, the GTA library has a document called 'Tims ORing Information'.  I don't know what the info was, as the link has been dead for years, but some oring standard information would definitely be helpful to people working on an unfamiliar air gun.

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