Random heavy trigger pull...any ideas on why?

[medmo]

Check out the vid around the 8 minute mark.

https://youtu.be/I4GtXq2XXOI

[OlongJohnson]

Older S&W cylinders had two small pins that passed through the extractor star. The pins held the star in place to prevent rotation. Empties take stress off them when unscrewing or tightening extractor rod, which have very fine threads and be torqued tightly. With newer cylinders, using empties may not be needed, but I suggest using them anyway. Newer cylinders' stars are shaped differently to hold stars in place.

Even better than empties are gage pins. They are precision-ground steel, sized every 0.001". You can get them to ~exactly match the ID of the chambers, which supports the extractor even better than empty cases. Often just a couple bucks each on Amazon. Get two of them. Better than the Brownells holding tool as well as cheaper.