Robert: I think you are referring to the "unhooking pin and spring" which will be depressed when the forend is in place. It is under spring tension and has a limited length of travel. See part 27 under the "Technical Information" tab on the left side of the home page.
The first point is that barrel removal is supposed to be an easy process.
With forend off, push the top lever fully to the right with your right thumb while holding the barrels with your left hand. This should open the gun as if you were to load it.
With the top lever still pushed fully to the right, push the barrels in an upward direction with your left hand.
Normally, that's it.
If you don't achieve separation, look into the open action and work the lever a bit left and right. You should see a square bolt (Part 15) moving in and out of the frame. If that bolt is not fully retracted into the frame, you can have difficulty removing the barrels. When the top lever is fully to the right, that bolt should be completely inside the frame.
Grunge in the action can interfere with gaining the necessary clearances to drop the barrels. If it is quite dirty, try cleaning the area and then try barrel removal.
Good luck.
I think this is the pin you speak of (on left front when viewed from below so right front from your description)
Jack
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