Hello on SAFETY:
That NPS Spencer Manual of Arms used a ROMANO Spencer, per Larry.
He did not recognize the person in the photo's.
As for safety:
ALL of Romano's Spencers have an "inertia" firing pin, meaning that when the hammer is at REST, fully lowered against the sliding striker bar that propels the firing pin against the reverse direction coil spring, the TIP of the firing pin does NOT project from the face of the upper block. Thus the block can be lowered without firing pin interference.
Also, with the hammer all the way down at rest, the action can be cycled to chamber a round with no firing pin-to-primer contact that would IGNITE the primer.
Yes, it is possible that some combination of weak coil spring, damaged firing pin and fouling in the firing pin cavity can cause even an inertia pin to fail and STICK BEYOND THE BLOCK FACE.
There is a 2006 Thread here about broken firing pins.
Larry has built upwards of 80 Spencers. He told me that he has never heard of one of HIS, with his design and materials, having any form of combination of a broken firing pin, firing pin coil spring failure or an accidental discharge while cycling when the hammer is fully at rest against the slider bar. Larry uses extra high-grade alloy, properly hardened parts, including, but not limited to the firing pin.
All that said, we should be experienced enough to never trust MECHANICAL features to prevent problems.
THE DESIGN OF THE SPENCER, especially center-fire versions CAN, DURING STUTTERED (forward/rearward) CYCLING OF A BALKY ROUND, ALLOW THE SOMEWHAT POINTED, FRONT SPLIT FINGERS OF THE CARTRIDGE GUIDE TO FORCEFULLY HIT AND IGNITE THE PRIMER! This HAS happened to me with primed DUMMY ROUNDS. Thankfully, the muzzle was safely pointed.
So, my respectful suggestion is to ALWAYS half-cock before lowering or raising the lever.
Historically, beyond Romano's, I KNOW that there have been DIFFERENT versions of so-called "inertia" firing pins in both after-market center-fire blocks AND "reportedly" in some Armisport/Chiappa reproduction Spencers. Strictly speaking, for safety reasons, I would NOT trust ANY OF THESE! I have been told that one prospective entrepreneur was talked out of supplying C-F blocks because of potential liability contingencies.
Certainly, KEEP THE MUZZLE POINTED IN A SAFE DIRECTION ALWAYS applies, especially if a part breaks and contributes to a discharge.
I had a late friend that was a legendary Federal Agent. He had a habit of practicing fast draw and snapping-in with his S&W revolver in his OFFICE, each day. He always unloaded his revolver and put the six rounds in an ash tray. Well ..... one morning he did not look to SEE six and only extracted FIVE due to a sticky round and balky extractor. He shot and killed his secretary on the other side of his office wall! Unsafe muzzle direction can create LOSS OF CONTROL. He had no answer about HOW the sixth round remained in the cylinder.
So "whether or not" should always be resolved AHEAD OF TIME in favor of EXTRA safety.
All the best,
El Supremo/Kevin Tinny