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

sizing o-rings QUESTION!


does anyone have a general guide on how to size o-rings?  For my specific question, I need to figure out what size o-ring to use for sealing a barrel or bolt.  Like the barrel o-ring inside an Mrod barrel, or the o-rings inside of a AF breech.  I'm not sure if I worded that well enough  ::)  Any help will be greatly appreciated!

Grab a copy of Parker’s O-ring handbook for more detailed guidance but a very simplified approach is to aim for about 10% squeeze for dynamic O-rings (those exposed to some form of routine sliding/friction).  For example, a -00x series O-ring has a cross section of 0.070” so you would want about 0.007” of squeeze.  Meaning 0.007” on the radius or a 0.014” difference between the diameters. 
How you want to approach it will just depend on what you have to start with…i.e. a bolt with some particular OD and/or a barrel whose throat is some particular ID.  Maybe they’re a good match (bolt 0.005” smaller than the barrel throat), or maybe not and you’ll need to turn down the bolt or enlarge the throat, or some mix of both.


Here is a link to the Captain O-ring printable O-ring size chart.  I have used this chart on several occasions with fair results.  YMMV.

Here is one


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