re:cerrosafe...absolutely get the casting out of the cavity as soon as it solidifys. It'll push right out.
Wait till it's cold to the touch and it'll be locked in place.
Do wait to measure it w/calipers or mic til it gets to room temp if you want a true reading. Otherwise you'll be getting that % shrinkage that allowed the easy removal while still hot.
Firing Pins,,,
Make the firing pin a nice rounded front tip. The total protrusion should be about .045" Thats more than enough to fire any cartridge and still not punch deep enough to pierce the primer.
I doubt springs were used to retract the firing pins. Most SxS's from the early to mid 20th cent that had separate firing pins from the hammers didn't have spring loaded pins.
The LC Smith side lock would be the closest to your Meriden in comparison and those were held in place by the stock wood and/or the lock. Taking the locks out of the stock and tipping the stock upwards on most LCS's will drop the firing pins out onto the floor for you.
Box lock Ithacas like the NID and the Nitro Specials have separate pins & use no springs to retract them. The Ithacas do use a set screw to limit travel of the pins in the frame but not for forward travel/protrusion. But rather rearward motion so they don't fall back and out of their seat from where they are installed.
Of the Meriden SxS's & singles I've owned (all 12ga) none had spring loaded pins.
These all depend on proper length of the pin (protrusion) and the small cut-out channel in each extractor to guide the pin back and out of the way as the bbl is closed so they don't jam the action.
A properly timed action with regard to the cocking arms/linkage will retract the hammer as the bbls are opened. That takes the pressure off the firing pin on a fired hull so there is no drag of the pin on the fired hull primmer. Removes any 'over the knee' opening antics.
