Originally Posted by LDBennett
If you make anyone of those components heavy enough then the bolt will not open at all. The area between wildly opening the bolt and not opening it at all is the timing and is controlled even in blowback operated guns. It can take time for the pressure to build to a point that it overcomes the inertia and the spring forces from the recoil spring and the hammer....
Having said that, it may be that the delay in starting opening can only be so great that the bolt will never fully open or so little of a delay that the pressures are too high and the case bulges as it moves to the rear out of the chamber. That is, the "good" zone is miniscule...
I believe we're thinking along the exact same lines here, and that the narrow "good" zone is the issue with the .17.
As far as when the cartridge actually begins to move to the rear... There is no locking mechanism between the bolt and the barrel. As soon as pressures rise enough to propel the bullet, force is being imparted in the opposite direction as well (against the bolt). Newton told me about this.
Energy great enough to force the projectile through the rifling is great enough to begin to move the bolt / casing to the rear, although with lower velocity since it has more mass to move. Nothing is making the bolt stay closed and wait until the pressures have subsided. The high pressures are the very thing that makes this kind of operation happen.
Perhaps my use of the term "immediate" can too easily cause confusion (Immediate in regards to what? The trigger pull? The hammer impact? The motion of the projectile?). If we really pick the timing of these events apart then nothing is immediate.
Again, I think we are in agreement for the most part, but are puzzling over semantics.