Remove the forend. Does the gun open easily now? If so, stone a little bit off the rear of the forend lug where it contacts the inside surface of the iron, a little at a time. Try it frequently as you go. Many new guns, Browning Citoris in particular, are shipped with the forend way too tight against the front of the receiver. This makes it feel very tight and hard to open while actually not holding it tighter against the standing breech. It's simply binding between the forend iron and the receiver front end. Don't wait for 50,000 shots. It may even gall between the two too-tight surfaces.
If it does not open easier with the forend removed, look elsewhere. Wherever you lube, use a good gun grease, not graphite. You'll be wearing the graphite.
