Several individuals of different boards got together to try to determine why so many US made trunnions have been cracking lately. The study was posted in full on the weaponsguild forum, and a slightly modified version on the militaryfirearm site. The differences between the threads is largely due to the input and photos from the membership on the sites, the data is the same on both. Photos of the trunnions tested are in a public photobucket account listed on the first page of the threads.
For anyone concerned about overheating the trunnion, they are carburized to a case hardness of approximately Rc60 at a depth of around .032". You can view a the study we just completed (without being a member of the site) here:
If you are a weaponsguild member you probably have already seen the full study but if you want to join to see it: http://www.weaponsguild.com/forum/index.php?topic=27074.0
A truly impressive amount of work went into that thread, and made for some very interesting reading!
Thanks for posting the link, but most of all, for putting the time and effort into it that you and the others did!