One of the most important aspects of owning a Mosin 91/30 is keeping the bolt clean and in proper working order. Unfortunately, there is not much information on exactly how to take the Mosin 91/30 bolt apart and put it back together. While there are some videos and a few pictorials, none of them explain the relationship of each part to its neighbor.
Two key pieces of gear for the Mosin that everyone should have are the bolt tool and broken shell extractor. The extractor is used to remove a stuck case that has separated its base from the rest of the case. The bolt tool is needed to properly set firing pin protrusion.
The extractor is used by dropping it into the chamber, then closing the bolt on the stuck case. Then open the bolt and pull the rest of the case out. Unscrew the extractor and discard the broken case. Put the extractor back together and it's ready for another round.
To remove the bolt, depress the trigger and slide the bolt out the back of the rifle.
Hold the bolt in your left hand with the bolt handle towards you and the bolt head to the left as in the picture below.
Wrap your fingers around the bolt handle and put your thumb against the bolt face.
With your other hand, pull the cocking knob and rotate it towards you. This releases the spring tension of the firing pin spring.
With the bolt in the fired position and out of the rifle, the bolt head and connector rod will come apart.
The large notch on the bolt tool fits the flat skinny part of the firing pin.
After unscrewing the firing pin all the way, the rest of the bolt will come apart. The cocking knob will separate from the bolt body. At this point, it's fully apart and can be cleaned easily.
The confusing part is, how the heck does it all go back together? Well, it's not as hard as it seems. The cocking piece and bolt body both have cuts that mate up as shown below.
Holding the two parts together, insert the firing pin spring.
Next, insert the firing pin. An easy way to screw the firing pin into the cocking piece is use a piece of soft wood to compress the spring and then use the bolt tool to screw the firing pin in a few threads. Once it catches, you don't need to compress it and can screw in the firing pin at your convenience.
All the Mosins I have seen have reference index marks cut into the back of the cocking piece. With the firing pin fully screwed in, use the bolt tool to line up the notches with the screw slot.
You can see that there is a square protrusion on the cocking piece. It fits into a corresponding notch on the connecting rod.
Slip the connector over the firing pin so the notch and cut line up.
On the other end, there is a small square that fits in a corresponding cutout on the bolt head.
Now rotate the bolt head so the little protrusion on the bolt head lines up with a corresponding cutout on the bolt handle.
There are 3 small notches on the bolt tool for measuring the firing pin protrusion. Use the tool to confirm the firing pin is set correctly. If not, use the bolt tool to twist the firing pin up or down so the center notch just almost hits the firing pin. Correct protrusion is shown below.
Now we are back to where we started. With the bolt in your left hand and thumb on the bolt face, and fingers applying light pressure to keep the parts together, pull the cocking knob and rotate it away from you.
Now you have the bolt back together and in the cocked position.
Holding the trigger down, reinsert the bolt into the receiver.
Hope this helps!