ive found they do lose air but the weight of the bolt is generally much more than the pellet so the 'moment' of force doesnt affect it as much as would be expected, most chases the pellet ..
It depends on the diameter of the sealing portion of the bolt (caliber), the distance it is inserted into barrel, and the air pressure used.
Energy is equal to force x distance but with all the losses in our systems, obtaining 1/2 that in the projectile is very difficult. So it’s a good rule of thumb to expect 1/2 or less maximum energy from this.
Lloyd has written a lengthy article on this particular bolt question some time back. Suffice it to say, it’s a very significant force, especially right beside your face. Especially when using larger calibers at higher pressures.
Likely if an ON barrel probe o-ring .... it will be displaced either blown out onto probe or gone forever. a LOT of noise that will startle the shooter. pellet/slug may not exit barrel
Reminds me of the time a fella goes to the doctor and says, "Doc, when I do this, it hurts" Doc says, "Well, don't do that!"
I was hunting once with one of my bottle builds and took a shot at a squirrel from fairly close range not aware that the bolt wasn't locked down - I got the squirrel, but damn near soiled my britches.