Note, I've used Speer Lawman for all of my reliability testing for ignition because it has a reputation for somewhat "hard" primers. I've also been using shims under the strain screw to adjust the trigger pull in double action. Measurements of pull weight have been done using a Lyman Digital trigger pull gage.
Model 620 with trigger tuned to 8 lbs. double action provides reliable ignition with Speer Lawman with the factory firing pin.
Model 610, a moon clip model, yielded a 30 % misfire rate in double action with the trigger tuned to 8.5 lbs, it took 9 lbs. to get reliable ignition with the factory firing pin. Prior to this I had installed the C&S extended firing pin and with the trigger set to 10.5 lbs I observed microscopic cracking in the firing pin dimples and 30% showed a darkened primer when the fired casings were trayed up. After the test at 9 lbs. with the factory firing pin, I re-installed the C&S firing pin and ran another test to see if it would causing cracking in the dimples at 9 lbs. with Federal Champion 40 caliber. That has not happened with the trigger set to 9 lbs., no primers show any darkened dimples. Due to interference with the grip screw on the Pachmayr Decelerator that's mounted currently, the 610 will have to be fitted with different grips before I can tune it any lighter. Once I get another 500 Magnum monogrip for the 610 I plan on experimenting with the C&S pin installed and see if I can get the trigger down to 8 lbs. in double action.
I suspect that most of the moon clip equipped models may benefit for the extended firing pin, especially if the pull weight in double action has been tuned lighter than 10 lbs. However, I strongly recomend that anyone using this firing pin keep an eye out for darkened primers. While I didn't have any primers blow out when my 610 was set up with a heavier DA trigger, that cracking I observed is a hint that the longer stroke firing pin wasn't needed. Basically, if you're going to tune your DA trigger weight, at some point you'll probably need the longer pin. However, with the factory weight, which in my case ran to 12 lbs. or more, this pin may cause primer penetration issues. So save your fired casings and line them up in a tray so you can quickly see if it too much of a good thing.
