Hi Chasdicapua:
It pretty much depends on the gun, unless the O ring is semi-floated in the sense that it can be blown out of place if no pellet present, I don't really see how this could happen...All O rings are set on deep grooves machined on the probes and fit very tightly...I would believe that if blown without a pellet they would most likely blow off with a pellet as well; the air pressure in the chamber immediately dissipates over a large open chamber & unobstructed bore when no pellet is present...I haven't done any specific testing but this is what my experience dictates me and I believe that manufacturers build their guns knowing that they will be fired without pellets intentionally or accidentally...I believe all of us have had no pellet air discharges one way or the other.
Some guns allow dry firing by not fully closing the bolt (Steyr is one of them) and some other guns have a dedicated air disconnecting feature (Feinwerkbau, Anschutz & Walther that I know)...Both of these systems are intended for practicing trigger pull & follow through while saving air and not so much for saving O rings...Actually it is a fact that air is disconnected because you are testing for vibrations and follow through impact around point of aim just after firing.
My Daystate doesn't have a dry firing feature and I can not turn the air cylinder 1-2 turns backwards for disconnecting air supply, so I either dry fire it when fully empty or with air and no pellet....I have never had an issue with it and this gun has a probe with an O ring in place as mentioned...
O rings being blown out of place is common when filling guns with CO2 cylinders or High Pressure Air and not opening the bleeding valve after closing the main cylinder's supply to the gun...People disconnecting the hoses out of their guns this way had the O rings blown out of the quick connectors but these O rings are semi-floating and flex inwards if not in contact with the male part of the hose connector...This effect doesn't happen when solidly held by a groove on the probe. CO2 and cryogenics are much more violent that air as they change from liquid to gas in milliseconds and this creates an explosion called BLEVE (Boiling Liquid Expanding Vapour Explosion)...it is this explosion what actually blows the O rings out of the hoses and this may also happen with the internal O rings in CO2 guns, I am not proficient with CO2 guns and I am just guessing.
I would suggest to find out if your gun can be dry fired when the bolt is at the forward point but before it "clicks" for fully engaging & closing, mostly all top of the line guns will not discharge air if the bolt is at this position but will dry fire...When the bolt is not at this position, upon firing it will be pushed forward...Not that it will hurt anything, but this is not dry firing per se and will not accomplish what you are trying to test for.
Hopefully this will answer your question...
Best regards,
AZ
