The Government's round - the M9 - was a steel-cased one with a cone-shaped nose.
It was single-loaded, and today, single rounds are quite collectable, as are full boxes.
In general, the M1911 is too heavy to reliably cycle blank ammunition - that's why you see the Star being substituted in 'The Wild Bunch' for the M1911 that would have been more realistic - but then, so little was realistic in that movie...
Successful blanks have been made from 9mm rounds in heavily-modified pieces, and sometimes from cut-down .30-06 rounds, as well - but they're hard to make, and more time is spent retrieving the brass (if reusable) than in filming.
The best place to ask this particular question will be a movie propmaster like 'Major 2' - he should have more insight.
Scouts Out!