Yup, 60% n-butane, 29% isubutane, 11% propane
http://www.vectorkgm.com/catalog/butane/Vector_Gas_MSDS.pdf
Edit: I purge the propane, though that isn't really an issue as it sublimes at a much MUCH lower temp than either of the other two, so it'd be gone long before the 'tane is.