Apparently when these were brought in years ago they were tested to destruction by the importer....the name escapes me, i want to say it started with a W....
Anyway, they apparently tested the guns up to 90000psi before they finally suffered "catastrophic failure." Which was not the gun blowing to pieces and takign the shooters face and hands with it, but rather the inside of the reciever where the lockign lugs on the bolt engage stretched or warped, makign it so that you could not open the rifle.
I'm searching for the appropriate article now...
EDIT: Found it
http://www.theothersideofkim.com/index.php/ggps/5637/
"Spanish “Guardia Civil” Mauser M1916 (.308 Win)
May 29, 2003
9:00 PM CST
This GGP is dedicated to Rick Lucas, with my apologies.
Shortly after WWII, the arms factory at Oviedo converted a number of the elderly 1916 Mausers from 7x57mm to .308 Win, for use by the Spanish Civil Guard, and fine-looking rifles they are too.
I read somewhere that these rifles were to be treated with circumspection, because the metal of the breech and receiver might not have been able to handle the added pressure of the more-powerful .308 Win cartridge, and I’ve mentioned that little snippet on a couple of occasions on this site.
Well, apparently I wasn’t the only one who thought this, because a bunch of Guardia Mausers were sent to H.P. White, a testing company, and tested to destruction. The SAAMI maximum of 55,000 psi (lbs/sq.in.) for the .308 Win was exceeded—and the rifles were finally destroyed at 98,000 psi!
In other words, I was talking total nonsense, and these rifles are perfectly capable of handling the .308 Win cartridge. My sincerest apologies to all, and to the Guardia Civil Mausers too.
The M1916 is based on the M1893, with a shorter barrel (21") than the older model. Possibly because of the rumors of their weakness, they are selling way below what they are really worth. The typical price is around $130 - $150, which is a steal. So if you see one and need a rifle in the wonderful .308 Win caliber, grab it.
(And everyone should have at least one .308 rifle—it’s possibly the greatest all-round cartridge ever made, and is certainly one of the most accurate cartridges ever made. And, as I’ve said before, everyone should own at least one Mauser, so with the Guardia Civil model, you get a twofer.)"