I'm afraid that I can't help much because I only own a Model 25-2. But according to the "SCSW 5th Ed.", the Model 25-5 was released in 1978 and continued until the 25-6 was introduced in 1988. Since the triple-alpha serial number prefix began in 1980, a 4" Model 25-5 could certainly have a triple-alpha s/n if it was manufactured between 1980-1988. If you're looking at a later 25-5, it would be a triple-alpha, but it won't have a pinned barrel since the pinned barrel was discontinued in 1982. Hope this helps.