This, seriously, depends on the type of ball you use.
As far as I'm aware,
ALL ZB's actually come in two halves, so that's not a serious consideration. Also, I've never come across a ZB that's
not made out of aluminium, so the weight of the ball really shouldn't figure into the equation at all.
But - and here is a BIG but...
You need to pay serious attention to the way the gimmick is attached to the ball. Most that I've seen have a cork-type affair (I hope you guys with Zombies will undestand what I'm talking about here, without me tipping anything).
Some of these are very snug-fitting, and will cope with the additional weight of a card deck, with no problem at all.
Other's however are 'loser', and you may find, especially if the deck suddenly shifts, due to the ball being re-oriented, that the ball will start to work loose from the gimmick
In reality, the very best way to test this out is through serious practise with the set-up. Please remember, too, that whilst a deck of cards doesn't actually weigh 'they much', in your hand, the actualy weight of the extra load on your finger will seem much, MUCH more than you'd imagine (I used to load with packets of sweets, and it really is pretty surprising how much mure you need to build you finger-muscles up).
I'm guessing, since you're asking, rather than actually experimenting yourself, that you don't actually own a ZB yet, in which case, I highly recommend GOING to a bricks & Mortar dealer, where you can see the ball/gimmick, and run through the idea with a dealer in person.
Hope this helps!
EDIT: Sorry - also meant to say - yes, 5-6 feet is a fine performance distance for adults; unless you are very good with your crowd-control, DON'T try this kinda distance with kids
