Its all in the length
The original setup (blank booster & guide) for shooting blanks was for 30.06....Sarco sells them. You'll find that the front cartridge guide is quite fat, as it has to make up for the loss of the bullet length.
This is the same logic for when you are shooting live .308, 8mm, 7.62x54r, etc., they all require a specific size front cartridge stop.
As far as shooting .308 blanks, people seem to use an existing booster and weld a plug that's tapped for a drilled set screw into the end.
The .308 front cartridge is also a homemade creation, apparently the Isrealis never fired blanks. Also, the .308 blanks now available vary in length...straight neck or crimped neck. (30.06 blanks seem to be available in only one length)
Anybody got a source for these different .308 blank cartridge guides?