I tore 3 casino decks yesterday.
Today I tore 4 casino decks -
I added 6 cards to one deck and tore it with pretty much the same effort as a 52 card deck.
Tore two more full decks - quartering one of those halves and then tore the 46 card deck and quartered one of those halves for a total of 4 decks.
I am finding that I am not getting the tear in the middle of the deck but the tear is higher in the deck. Looks like I need to fiddle with my set up and hand positioning.
More training later...