To echo others, I almost always land at B from BHM, a flight I take 1-2 times a month. Furthest gate to furthest gate might make it a mile in all, however there's a tram between concourses that makes the trip shorter. Hopefully, they're not in the back of the arriving aircraft or heavily burdened with small children or massive carryons. 50 minutes is very doable, but I wouldn't stop for a souvenir.