The only times I've seen brass flow is either due to running high pressure, or using soft brass. High back thrust can cause damage to the locking lugs of a bolt and or the mating lugs on the action, but IMHO back thrust is a completely separate issue than brass flow.
I would suggest trying a different brand of parent brass to see if the issue persists. If it does, I'd look at backing down your loads.
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The brass case acts as a plug to seal chamber gases. If the chamber is rough 'not highly polished' effectively increases the surface area of the chamber. Many 'smiths' will run a little scotch brite in the chamber as a final finish after reaming. Also, running 000 steel wool on the case doesn't hurt either.
Yes the case ( if supported well enough by the chamber and blot, and within its limits) will balloon, and seal everything off. The pressure force acts in all directions. If the area of the chamber is increased more force, PSI X area, acts against it, (the chamber). Still the back thrust against the bolt is PSI X case head area. Or maybe area of the bolt face it self, if the case doesn't seal or ruptures.
I'm really not trying to argue with you that know what you are talking about. I have followed this being disused before. I am curious about it. And trying to get it explained to me. Thanks.
