TW - given time and some of that on CAD (
)I could show some aspects graphically. But for now I will attempt (operative word) to do this thru description.
That ''cup'' in the frame is actually receiving the barrel lug base protrusion at fully unlocked - at which point it actually
could prevent feed ramp from being any further back than level, with the mag' well. It is tho not designed to take that much of a whack!
Coincident with that at unlock is the actual and theoretically main limiting factor - the pin, in the lug slot. That should prevent the barrel setting back any more on it's own so - the ''cup'' is actually a clearance device shall we say.
Now, also at unlock the barreland lug is at its lowest point, having dropped, thus the contact with the wear areas we have seen by the exterior of chamber profile. I say contact - in fact from a design POV I expect with the incredibly tight tolerances in this gun, we have a theoretical ''barest kiss''.
However, if we consider the extreme violence of the event (firing) during a full cycle - it seems very likely to me that a two or three thou over travel downwards, and maybe a thou or so to rear (heck, this is a demanding gun to design!) - and we can see the slight attrition to the surfaces and thus a very small flake or two of displaced aluminum.
I still feel this is self limiting and I guess if tolerances were sloppy as heck, it might not even happen. Now remember folks - this is me theorizing and not Eric taking. That will come later when we have full answers!!
Looking at the whole cycle and so recapping a bit (heck - wish I could animate a Flash file like the one on a 1911) ..... I can ''see'' it clearly but description in words is a bugger!
At instant of slide beginning rearward travel as round fires and pressures begin to back off from peak, we have the barrel moving rearward by approx 1/4", as recoil assembly is being compressed by slide - (exerting as it does said rearward bias against barrel lug) - at which point the lug slot allows it to drop, and there it stays while slide goes all ways to rear.
Slide progresses then forward, stripping a new round - which is fed into the lowered barrel and chambered, assisted by the feed ramp. The completion of the auto load is aquisition of full battery and as slide moves further forward, and recoil assembly is (relatively) relaxing, we see the bolt face area impinge on the round's base to complete the action. The last 1/4" or so as round goes into battery and slide closes, is when the lug slot then rides the pin to lift chamber area (barrel rear if you like) once more and go into full lock-up.
Phew - if you understood any of that it's a miracle. How useful an animation would be!! Just don't have the time.
See if this fits in TW with any thoughts you or others may have had. I am as ever verbose and rambling - but this is not that easy to describe so as to make it foolproof to understand!
