Here's a schematic.
The plunger may be damaged or the tunnel may be fouled.
If you can grab it just pull until it comes out. new plungers are readily available from Gun Parts.
If you can move the plunger almost out, but the enlarged head is stopping near the front of the tunnel, it's possible the front edge of the tunnel has been slightly battered and compressed, You may need to lightly bevel the edge to open it back up to original condition.