Help with carbine tubes

[emmab]

Hello I was wondering if anybody could tell me if all carbine buffer tubes(rec. ext.) are the same length? I'm in the market for a collapsable stock and would like to get the shortest possible when collapsed. The specs I see can range from 7 -10" with stock on when collapsed. Is it the tube or the fit of the stock that changes these specs? I realise that some stocks will be longer in construction ie butt pad and so on and maybe the hole for the tube stops farther from the end of some stocks than others. Cheers and thanks in advance