If you can afford a custom-built shotgun, it’s absolutely worth it. During a fitting, every part of your body that matters to the fit of a shotgun is measured so that the gun acts like an extension of you, not an 8-pound piece of metal and wood you’re holding against your shoulder. The experience of buying a bespoke shotgun is traditionally done in Europe. In America you can initiate the process by finding the right dealer. For instance, Beretta has its own gallery with locations in New York City and Dallas where you can be fit for a bespoke O/U.