Your just dealing with something that everyone has to deal with when shooting a 50 BMG or any large conventional chambering when using a muzzle brake.
Its not the recoil that is making you flinch, its the muzzle blast which you can actually feel on the shooters face. When I started shooting the 50s, I was comfortable shooting with my mouth slightly open. Just happened when I relaxed and concentrated on shooting. Never had any issues shooting smaller chambered rifles, in fact did not even realize I was doing it but when I would touch off a 50, I could feel the muzzle blast in my teeth, literally and I did not like it.
You can also "FEEL" the blast on your forhead, cheeks and chin, MUCH more then anything else out there, just part of shooting the big rifles.
One thing I have found that helps is to make sure you wear a good set of shooting glasses which will block alot of the area around your eyes from the blast. The eyes are very sensitive to muzzle blast so the best way to do this is to block that blast with glasses.
Also, If its a recoil issue, I would recommend you order in some lighter weight bullets for practice. Something like the M33 ball in 647 gr FMJ will REALLY cut down recoil. I am shooting these in my AR-50 for a plinker load and if you sort bullets, they are suprisingly accurate, its nothing to get 1 to 1.5 moa accuracy with new M33 bullets if they have been sorted at ranges out to 1500 yards or so. Recoil is dramatically dropped and it will help you "TRAIN" your brain to what the 50s present when fired, its a totally different game.
As far as more effective muzzle brakes, there really are not many better then the Barrett brakes other then the Armalite AR-50 brake but the AR brake will increase muzzle blast to some degree.
That said, the AR brake has blast sheilds that protect the shooter to some degree, at least opens up the protective cone from the muzzle blast a bit better then the Barrett. If you look at the AR-50s muzzle brake you can clearly see the blast sheild, I can not imagine it would cost much to have something like this made for the Barrett rifle and just sandwich it between the brake and barrel to help protect the shooter from blast.
But as far as reducing recoil, you have about as good a brake as there is out there for the 50 BMG.
Again, if recoil is causing the blink, practice more with the 647 gr bullets to train your brain, and eyes and also cut your string length down. Your body it telling you something if your starting to blink. If your blinking, your likely flinching. That is if your blinking before the trigger breaks, if your blinking after the trigger breaks, your worrying about nothing. I do not know anyone that can shoot a 50 BMG and not blink after the trigger breaks.......
You may be worrying about nothing.