I have a model 65 3" that jams when rapid firing .357 rounds.
The gun is lightly used and locks up fairly tight.
Any suggestions as to problem?

Did someone replace the trigger return spring with a lighter one ? If so you might need to go back to a stock spring.

Also check your sideplate screws.

I have a 65-3 that, when I first bought it, locked up when firing 357 magnum rounds, but not when firing 38 spec. We found the problem to be a loose ejector rod. I believe it screws tight counter clockwise, but I may be wrong. Check it out.

Lockup of the K frame magnums under continuous fire with magnum ammunition is a known issue. If you really feel you have a need for this, contact the factory and/or Performance Center at the factory.

[I believe, but do not know for sure, it's due to heat expansion of the stainless steel in a couple of critical areas.]

Make sure you are allowing the trigger to come fully forward after firing. If you do not you will reach a place just short of full trigger return which will completely lock up the action when you try to fire again. This happens in rapid DA fire and is more common in guns which have lightened springs. It's also easier to do accidentally than it is on purpose(as when you try to duplicate it deliberately). Concentrate on letting the trigger slam forward, after lots of shooting your muscle memory will take care of the problem without thinking of it.

If this is the problem you're relating your gun is ok as long as everything else is working as described.