I have A300 & A301, both owned since new & close to 45 - 50 yrs old. When steel shot came to be necessary for waterfowl I had choke systems installed. I had the work done by two different gunsmiths a few years apart. I neither case did not specify to gunsmith what choke system to use, & in both cases they installed Colonial Arms thin wall, with a extended modified choke. I later ordered extended Improved Cylinder tubes directly from Colonial Arms. These are quality shotguns & have worked great with that set up. Two of my grandsons now have them, & are their main waterfowl guns. As both guns have 3” barrels neither gun always functions consistently when using low fps lead shells for casual clay busting or upland hunting, but just keep it clean & up the speed a bit on the shells & they work fine.
Many years ago I owned a 301 chambered for 2 3/4” which worked perfect for upland with whatever lead shot was available then. Sadly I traded that Beretta 2 3/4” on something shinier.
Both gunsmiths did not recommend reaming out the chokes, but that was a long time ago so maybe techniques have changed. I believe that only aftermarket installed thin wall choke systems are acceptable options for these Beretta barrels. Cannot find Colonial Arms web page so guess the only option is Briley. As others stated Lots of $$$.
I recommend being patient & wait for 3” barrel with choke system installed or set up in a modified choke. Also could consider stepping down to 2 3/4” barrel with either choke system or modified choke. While the 2 3/4” barrel will not allow for using 3” shells there are 2 3/4” steel shot shells available & this barrel would enable dependable use of all low fps shells. And yes Browning B80 barrels will interchange.
They are great guns & well worth getting into a configuration that works for you.