W W Greener, The Gun & it's Development, 9th edition page 242 "A barrel eaten right through with rust, ""At or Near the Muzzle"" may be fired with perfect safety.
Quotes mine, that would be somewhat akin to "Magna-Porting", which incidentaly he mentions on page 513, though calling it "Perforated".


Miller/TN
I Didn't Say Everything I Said, Yogi Berra