I also made some card sleeves as you described with good results with birdshot. Bigger balls (.40 that is or buckshot) weren't too good. I'll try to make some liek the old Alcan kwik sert but with card. I made a couple, fold the card in half, fold the bottom (middle) again, some scissor work and voila. Tedious work sure, didn't shoot any yet. Will grab all the pics I promised and post soon.