I am still confused.
Yes the gun gets hot , I don't deny that.
I have shot 16 rds of skeet in one day that is 400 rds using the same gun. I have also run 200 rds of slugs or buck personally thru the same gun. My guns have also not only had me shooting them - but others as well.
I know for sure my SX1 has had 1k rds fired in one day, so has various 870s.
NO biggie for me to run 2K rds in a week, out of the same gun, without cleaning and no malf's.
Now granted after the chamber gets a bit dirty, there may be more residue on spent hulls , be they new shells [ slugs, buck, target] or reloaded shells.
"Melting" ...no. I have had the end where crimps are blown off, get a hole burn thru, and such - these were reloaded quite a few times and probably I should not have reloaded them "one more time".
Then again I have not shot some of the new stuff, I do not like the new AA for instance- so perhaps standards have changed for the worse.