those who leave air spaces in bp cartridges do not do it to be different or start a trend etc..
they have read articles and books by gun makers like mr greener and others.....so its not taken lightly.
one chap i know shoots competitions all over europe and fires 1000s of rounds without incident or chamber ringing of any sort.
myself i stick to using kapok as i only shoot bp occasionally.
remember many people still use cream of wheat in bottle neck cases and dont realise they can cause case / neck separations and have been shooting that way for years without incident......pays ya money and take ya chances