OP has sent some pictures - it is a Spanish Guardia conversion to 7.62 NATO - small ring, with "anti-bind" ridge within the left bolt race way, so possibly originally a Spanish 1893 or 1916 or something like that, Guardia ("falangist") crest on receiver, set into a sporter stock. The receiver has serial number 3Z ###X, and is marked CAL 7.62. The barrel has the thinned shoulder at the receiver, so barrel was set back for the re-chambering, when the barrel was re-bored to 30 caliber. Interesting to me, the receiver has NOT been drilled or tapped for scope bases. Compared to pictures in MMROTW book, the rear sight on the barrel appears to be like the Spanish Model of 1916, Second Pattern.