Just a couple of points:

1. The pin that locks the cylinder into the frame is the "Center Pin"
2. The other locking point on the J frame is under the front of the barrel, the spring loaded pin is the "Locking Bolt"
3. If the Locking Bolt is not properly fitted it offers no real support for the extractor rod/cylinder. This makes the Center Pin the actual and sole locking point for the cylinder. One thing to check on any S&W revolver is to look at the front of the Yoke while in lockup, hold the frame with one hand and try to move the cylinder laterally with the other. If there is more than just the slightest play, the Lock Bolt may not be doing its job or there is already some elongating of the Center Pin Hole in the frame. If the Locking Bolt is not offering proper support, the Cylinder Pin is taking all the pressure and wear and tear. This will probably lead to accelerated wearing of the Hole in the frame.

I think many folks don't appreciate the true roll of the Locking Bolt and importance of its proper fitment . FWIW

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1st Signal Brigade, RVN '70