I don't know where you get your info as follows:
"when the rifle is fired, the brass actually expands under pressure and produces a "friction bond" between the chamber and brass. I understand this keep the head of the brass from contacting the face of the bolt (or reciever in this case i guess) to harshly."
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While the expansion of the case "may" help, it is my beilef (right or wrong) that headspace is the bigger culprit in how hard the brass smacks the bolt face or breach face.
In essence, if you have too much headspace, you are litterly moving the brass forward with the firing pin, then once the primer goes off firing the round, you are driving the brass backwards with a good bit of force.
The more headspace, the more violent the counter-force is and the more noticable the signs of "pressure" are noted.
I had a Colt Gov. Model in 9mm once that I got from a fella who had not shot it much at all...even gave me the rest of the box of ammo he purchased with the weapon. When I went to qualify with it as a duty weapon, I noticed that the primers were flattened so bad you COULD NOT distinguish where the primer ended and the brass cse started. It would also completely remove the chrome plating on the primers and ELIMINATE the headstamp markings on the brass where they stamped in the brass brand and caliber.
Come to find out, I did some comparing that night and discovered that the factory had reamed the barrel for 38 super auto and stamped it as 9mm. In round figures, the 38 super auto chamber is about 1/10" deeper than the 9mm.
Colt gladly replaced all the parts and even threw in a couple new clips as well.
Just my $0.02