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The bolt-action Spanish FR-8 was a stopgap firearm, thrown into service by the Spanish when they were already moving toward the 7.62x51 mm NATO-chambered Cetme rifle. The FR-8 shares the later rifle's chambering, and actually appears to be a gas gun, though the tube is simply storage for a cleaning rod. For more on this unique piece of history, check out this "I Have This Old Gun" segment from a recent episode of American Rifleman Television.
Great powers have often used smaller conflicts as test beds for new weapon systems, and also as dumping grounds for obsolete machinery. The Spanish Civil War was one such conflict.