If you remove the fore end ( depress button and slide forward, to slide it loose. If I remember correctly, you have to sort of slap the forearm forward more than once. as the fit is so precise), you will see stampings on the barrel. It reveals the "grade" of the shotgun. It may help you identify your shotgun better for finding the answer / part.
Add 10 to it- to the number of stampings, to get the final grade. (ie. "4" stampings, **** plus 10 makes it a grade "14".
oops, Wrong advice, wrong shotgun. Sorry. To remove the barrel, you tap the muzzle backward to the breach. I knew there was tapping and sliding involved, just forgot the details. I apologize. It's been 30+ years since I handled one .
Be very careful disassembling a Darne. The higher grades have a button under the forend. You open the action, depress and hold down the button and then place the muzzle on a rug and give the butt a sharp slap with your hand. Be careful to catch the barrels when they come loose. On the lower grades, you have to depress and hold down the spring inside the action (it's clearly visible and has two small prongs on the front end) while slapping the butt. Don't let the little prongs catch the barrels when you do that, as you can break that spring and they are wicked hard to replace.
There are three different models: R, P, and V. Normally, the Rs are grade 10-16, the Ps are 17-18 and the Vs are 19-22 and custom grades. I own one grade 10 (a very rare 10 gauge) and one grade 19 (something of an oddball, as it's a P model, not the usual V model), so I have experience with each of the different styles.
Apparently, at least according to recent postings on the Doublegunshop.com BBS, someone has bought the Darne name (I'm not sure what happened to the Bruchets, who previously were making Darnes) and production facility and is manufacturing a very limited number of Darnes.