Do you mean a shotcup without slits in it? if so yes, but you have to cut slits in them or they will hold the buck shot together all the way to the target. If you are looking for wads without a cup there are plenty to choose from made from cork, vegetable fiber, cardboard, felt, and plastic as well as those you make by removing the petals from field wads. It doesn't matter that your overshot card is 1/4" inside the hull either. Check out http://www.ballisticproducts.com/ and http://precisionreloading.com/
Even finding plastic shot-cup wads that fit brass shells is going to be a problem.
The walls are thinner then a plastic hull, with no taper towards the base.
I believe a 12 ga brass hull would need an 11 ga plastic shot cup to seal properly.
I think Ballistics Products might have something, but that's the only place I know of.
They do have a brass hull reloading guide booklet I think, and that would be a real good place to start.
You might gain something by using Grex plastic buffer with the shot.
And hard shot, or plated hard shot.
And Mylar wrap around the shot.
They have all that, I think.
Not fully slit petals will help, but no slits will not release evenly and will skew the pattern. I can tell you now, the bigger the shot, the harder is is to get a tight long range pattern, and 00 is about the biggest. I spent thousands of dollars on barrel work, and shot untold patterns, and I never got BB to pattern as tight as #1 or #2, and I never got that to pattern as tight as #3 or #4 shot. I got real close, but it took a heck of an effort, and all I got was close.