the brittle recievers were caused by a primitive heat treatment process and for the most part many of the ones prone to failure have been weeded out over the past 100 years. rock island armory changed their heat treatment process around serial number 280,000 and springfield changed theirs around #800,000. your rock island armory is safe to fire. generally speaking it is in great condition and should be a good shooter assuming the bore is not rusty. it was made roughly around 1919 and it was rebarreled with a springfield armory barrel at some point. .
I am not an expert of proofs and cartouches but they are pretty much just marks that show that it passed inspection before it left the factory and again before it entered service. IIRC, the SAA stamp on the stock I believe stands for Springfield Armory and the Ps are idividual inspectors marks
ignore my complete lack of capitalization. I still have no problem correcting your grammar.
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