sizing o-rings QUESTION!

[YEMX]

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!

[nervoustrigger]

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.

[rdtricks]

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.

https://www.captainoring.com/supportmanuals.html

[IOWOLF]

Here is one