You have a 5 screw .38 M&P Hand Ejector Square Butt shipped around 1909. This is also known as the Model of 1905, 1st or 2nd Change. The N stands for nickel which is how your revolver is finished. It has had either a replacement barrel installed or the original barrel was cut down from the rear and rethreaded which is how it might have lost the locking lug. It is a K frame gun and any grips made for a K frame should fit. To be original, you need a set of pre-WWI walnut checkered diamond around the escutcheon with a rounded top -- no medallion.

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SWHF #474 SWCA LM#2629