I've got a Bushmaster with 11.5" barrel and 5.5" car style supressor. What sort of surplus ammo should I use?
I'm looking for something for general all around use. I'm sure its been asked before but I'd appreciate any help.

What twist?

I'd suggest SA battlepacks.  

1/9 twist

I would recommend q3131 or xm193 for all-around use.  If you can stock some extra stuff, you might want to look into heavier loadings for personal defense roles.  Either 68 gr Black Hills Match BTHP, or the 69 gr Sierra MatchKing.  Out of that short of barrel, your velocities are obviously going to be much less and your effective range for fragmentation from mil-surp ammo is probably less than 45 yds.

I could be way off since I don't have a shorty but that would be my suggestion.

Thanks for the help.