Howdy
Without detailed photos it is pretty tough to say anything about the OP's Iver Johnson.
However, I can offer this bit of advice. Around 1900 Iver Johnson completely redesigned their line of revolvers. Prior to these design changes, the older Iver Johnson revolvers
were not safe to fire with modern Smokeless ammunition, I don't care what anybody else tells you. After the design changes Iver Johnson revolvers were safe to fire with modern Smokeless ammunition, as long as the gun was in good condition and functioned properly.
There are three easy ways to tell a Black Powder Only Iver Johnson revolver from the later Smokeless models.
This is an earlier Black Powder Only model.
1. The little owl on the grips faces forward.
2. The shape of the locking notches on the cylinder shows that the bolt only engages the cylinder on one side, the hand is what keeps the cylinder from rotating backwards.
3. If you remove the grip, the hammer spring will be a flat, leaf spring.
This is a Smokeless Iver Johnson.
1. The little owl faces backwards.
2. The locking slots on the cylinder engage both sides of the bolt, the cylinder does not rely on the hand to prevent backwards rotation.
3. If you remove the grips, the hammer spring will be a coil spring.