The primary limiting factor to the breech pressure attained in the 10mm is not the standard (i.e., unramped) barrel, but rather the case construction.
Remember that the 9x23 Win (55K PSI) was successfully produced in the standard Colt 1911 GM without a ramped barrel. No blowups as far as I know, but a suitably constructed case.
Yes, my investigating says Winchester brass is the strongest, though hard to find, sane loads in a ramped barrel should prove Starline to be just fine too.
