As observed, we don't have a U.S. Proof House, but are blessed with an abundance of lawyers specializing in Class Action.
It is likely that the barrel proving protocol at Remington was buried in non-disclosure as part of the Garza Settlement.
Interesting that the Loitz index case of 1983 was a 1100 Trap gun bought used, and shot with hand loads.
Loitz vs. Remington Arms
http://www.leagle.com/decision/1990960563NE2d397_1953.xml/LOITZ%20v.%20REMINGTON%20ARMS%20CO.,%20INC.
Garza Class Action
http://www.gunsmoke.com/guns/rem_lawsuit_intro.html Settlement Announcement
http://www.gunsmoke.com/guns/rem_shotgun_lawsuit.html I've had no success looking for a descriptions of the barrel testing procedure used by any U.S. maker. Winchester used "loads far exceeding normal power."
The Remington Proof Loads used by Sherman Bell and Tom Armbrust were reported to be 18,560 psi.
