A number of possible reasons:
Slow powder, light bullet, less than a compressed load. Primer did not create enough pressure to get the powder ignited. Most common with standard primers and ball powder. 4350 is not difficult to ignite, so probably not this issue.
Bullet seated long and engaged the rifling and kept the case shoulder off the chamber shoulder, cushioning the blow. Not likely with such a light bullet.
Oil in bolt and cold weather. A primer is ignited with shock (high velocity hit). Cold oil can slow down the firing pin. The dent shows energy, but not velocity. Squirt some G96 or brake cleaner through the bolt.
No powder in the case. If the bullet did not pop out of the case, this is a good bet.
Primer not seated deep enough to bottom out the anvil legs.
Defective primer.
Pull the bullet. (I use pliers and the die hole in my press.) Is there powder? Virgin powder? Means primer did not fire. Yellow or lumpy powder? primer fired but no ignition.
Deprime as normal and examine the primer. Did it fire? (Don't worry about the primer. You could not set it off if you tried.)
Please report what you find.