All the 'slam fire' stuff aside,,the 97 does have a 'firing pin lock' inside the bolt.
That may be the problem if you are not unintentionally doing the above and not realizing it.
When the bolt is closed and locked,,the firing pin lock is disengaged and allows the firing pin to move back and forth so the blow of the hammer can fire the cartridge.
When the bolt is first unlocked by action of the op-rod, the firing pin lock first allows the firing pin to retract by power of the coil firing pin spring.
Then that 'firing pin lock' engages the firing pin and holds it in a retracted position all the way through the bolt cycling.
This so the firing pin cannot protrude from the bolt face as the bolt is closing and fire a round (slam fire) w/o pulling the trigger.
(This would be a true 'Slam Fire')
That firing pin lock can become worn. It can become rusted in place and not work as it's intended to do.
There are two styles: Old style powered by a small flat spring. New style slightly different shape and powered by a simple small coil spring.
If the Firing Pin Lock is the culprit, then the firing pin itself could also be involved in the problem.
It too may be stalled in place with dirt, old oil, rust, crud, it's coil return spring damaged and not doing it's job.
Some or all of this can lead to the firing pin staying in the forward position after firing and not being retracted by it's spring. Then the Firing Pin Lock if it doesn't do it's job leaves the firing pin hanging out the front of the bolt.
With enough resistance to fail to retreat into the bolt as the bolt is closed on a loaded round you can experience a 'Slam Fire' of the true kind.
You need to remove the bolt from the gun to get at it and the firing pin.
The type of slam fire mentioned in the other posts is just the trigger mechanism design. There is a disconnector in the action. In this case it's the carrier and it's relation to the hammer.
The hammer w/o a disconnecting action would just follow the bolt down as the action is closed.
Same on the M12,42, ect.
Each of these uses a slightly different design, like the M12 uses the bolt lock arm. As the bolt closes, the bolt lock arm drops out of the locked position. That allows the hammer to drop from the dissconnect position to the cocked position as it normally does.
But since the trigger is pulled and the sear is down,,the hammer continues ahead and fires the now locked gun.
But they all insure that the action is closed and locked before the cocked hammer is released and drops to fire the gun.
Even the little M61 .22 pump gun will operate the same way.
Hold the trigger back and pump away. You can scatter .22's all over the landscape. Good bunker clearing tool for those woodchucks.
It's just a simple design that's all.
No magic,
It's actually a simple trigger mechanism from a closed bolt full auto system.
When Browning went to make the Repro Winchester M12 and M42 shotguns in the 80's(?),,the lawyers made sure they included an interupting 'sear'.
So the trigger must be released and then pulled again before each shot. No 'ata-matic' pump guns no more.
I think the Ohio made Ithaca 37's are that way also.