I prefer trial by fire. Start your own server, pick a support class, find a fixed object or small sign on a wall somewhere 20 yards away from you and go FULLY AUTOMATIC on it for a half or full magazine. Repeat this 20 times, each time make small adjustments to keep your grouping tight around that object. Just get a feel for the weapon at fully auto. After 20 attempts you should have noticeably better recoil control, and then do it another 20 times and continue doing it over and over and over, and then find new objects, walls, or signs and do it another 20 times. You'll be threading needles with your BAR after an hour of this, and then it's simply a matter of translating your practice into server play. Practice is repetition, skill is the result of that repetition. If you can master recoil on the support weapons then you can do anything.