I would say that it is a .38 M&P model of 1905 3rd change. Apply a little Kroil or Breakfree in the empty screw holes and under the sideplate after removing the stocks. Let it soak and then try the methods mentioned above. Strike the grip frame where the stocks would normally be while holding the barrel in your left hand (assuming that the hammer or wood dowel is in your right). I usually wrap the gun in soft leather just to be safe and hold the side plate over a pillow or something soft just in case it drops off.

Clean the internals with your favorite degunker and then apply a small amount of machine oil. Reinstall the sideplate carefully and reinstall the screws. Keep track of which screw comes out of which hole as they are not all the same. There are several videos on Youtube that show you this proceedure. Best of luck.

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James Redfield
LM #497