This battle is, again, due to injury history of Buffalo's projected starters at the tackle position.
With Cornell Green set to start at right tackle, whoever is the primary backup had better be ready for action. Green has played 11 seasons in the NFL, and has only played a full season in two of them. Over his most recent three-year stint with the Raiders, Green had one full 16-game season, and missed a combined 10 games over the other two.
The swing tackle battle really comes down to the starting left tackle battle. If Jamon Meredith beats out Demetrius Bell for the starting job, then Bell will likely take the swing tackle role. If this happens, then Bell would likely get some starts only at right tackle, as Meredith has proven quite durable, never missing a game during his two years as a starter at South Carolina and not missing a game due to injury last year.
If Bell wins the competition, however, then Meredith could wind up seeing extensive action at both spots, with Bell coming off a torn ACL and remaining an injury risk.
Ultimately, I believe Meredith wins the starting gig, leaving Bell to the swing role where he will likely get a few starts at right tackle during the season.