#6 lead shot weighs app 2 grains per pellet.7 pellets tamped into the end of the ferrule shouldn't take up much length but I'm not sure exactly how much.I have put 7-8 pellets into the hollow cavity of a steel adaptor without tamping.If you are shooting wood shafts,I would think tamping them in with a small steel punch would be a good idea.Just looking at 6 of these shot,I doubt you would lose more than 1/4" of ferrule length if you tamped them in,possibly less.You can also get the fixture to drill into your taper and install a piece of nail,to add weight.