Hi,
I just replied to a thread about wadcutters at 25m.
With regards to card I find cheap pound land card - £1 for 30 sheets of light card works ok for wadcutters at rifle velocities. I put the card target directly on to of a card board box back stop. Using a pistol not so good - the lower velocity does not lead to clean holes. One important thing is not to get card so heavy your printer can not handle it!
Paper designed for water colour painting may be worth a try if not prohibitively expensive.
Frog