I had a friend tell me his buddy had a Argentine Mauser for a little bit of nothing.. so I went and looked on Wed.. I knew it was an 1891 and was sporterized, but the crest, I had never seen.. So, I bought it for the crest and drug it home, and little did I know.... what I had drug home.
Near as I can figure.. it's from The National Military College is the institution in charge of the undergraduate education of officers of the Argentine Army in Buenos Aires. There are 3 small lots of these rifles that exist, for Military School (125 rifles), Naval School (75 rifles) and University Battalion of the Federal Capital (University Battalion - 200 Rifles). Each has the schools respective crest stamped on their barrels. These guns will also have school serial numbers, the school serial prefix is different for each, and they usually will also have the standard serial intact as well. The military gave these schools rifles, and the schools, I'm guessing marked and serialized each rifle as such.
So...going off the schools serial B.U.18, this should be rifle 18 of 200, the school serials match, the originals don't. There is no import stamps, so either it predates import stamps, which is possible or the stamp was on the barrel stub that was hacked off. The receiver Argentine crest stamp was scrubbed, much like the very early imports of Argentine Mausers.
This is one, while I hate sporters, I was glad I got, I never knew Argentina had such a thing as officer cadet training schools, much less rifles dedicated to such training. Looking through numerous sources, info is few and far between on these, even photos of them are pretty scarce.