The 5" M27 was a popular sidearm even though many folks didn't know you could order or get the 5" bbl just by asking. Most often you found them in 3&3/4", 4" or 6" but there were a couple of gunwriters who favoured the 5" and wrote about them.
Yours is hopefully one of the older models ..... If you open the cylinder and look at the inside of the crane you should see some stamped numbers, such as 27, 27-2, 27-3, etc., and possibly the serial #, which will tell you what model it is. Yours should have a pinned barrel and recessed chambers if it is a 27 or 27-2 and if you have one of those I would keep it, shoot it and pass it on down to your children. JMTCW. Mikey.