Midscreen:
c.l, c.m. c.h, s, j.dh, air Shield Slash L, land, jump, j.dh, air Shield Slash L, Charging Star L, Charging Star H, Hyper Charging Star
Corner:
c.l, c.m, c.h, s, j.m, j.m, j.dh, j.s., Shield Slash L, Hyper Charging Star
I tried the corner combo with the Deadpool OTG assist and it did even less damage. I might have done something wrong?
You’re missing a whole 2nd half of the combo 
For Midscreen, do j.up H. j.dH does the least amout of damage. Plus, after your air L.SS before your charging stars, hit S and relaunch them into a MMHd.HS. Since you’re using Deadpool assist, call DP, backdash, throw an air shield if you reached the corner, then do your two Charging stars -> HCS. Or you can just do a standing L.SS > HCS. Should do around 720-750ish.
In the corner, the highest damage that I’ve found is, c.L, c.M, c.H, S > super jump backwards, j.uH, L.SS > jump back, j.uH, L.SS > dash under S > j.MMHd.HS > jump instant air j.LSS > L.CS > H.CS > HCS.
Have you checked out any combo videos on youtube? BrawlersUpTV has a high damaged unassisted combo video http://www.youtube.com/watch?v=rZ52XL-N19M
Captain America generally does more damage by hit confirming with an air S. Also, it’s better to start his combos with MMH… rather than LMH… though the former may not always be possible.
You should put how much damage it does. If you’re not getting at the very very minimum 725k, there’s big room for improvement. 750k would be about average for a decent optimized B&B and 800k is a good amount for a completely optimized B&B. My B&Bs usually hover between 725-750k just because I don’t have much time to practice the game.
I find combo video combos are generally fairly unrealistic. You have a much higher chance of hitting with cr. l than jump s and you don’t lose a ton of damage doing LMH rather than MMH.
I hate starting combos w/ j.S MMH. Only when I get a mix up, I will start my combo with MMH.
Try staring it with j.d+H. It seems to work a lot better with me.