Here's how I make my 20 gauge tube jacket slugs. Got a lot of inquiries on how to make them. So, here ya go. Right or wrong, this is how I do it.
Materials, 5/8 .050 wall copper tube, and pure lead cores.
1. Cut tube to prescribed length.
2. Place tube in jacket end rounding die, and close up one end with press.
3. Reduce jacket through sizer die.
4. Flatten end of jacket
5. Insert lead core and swage to expand core in jacket.
6. Point form nose.
7. Now at this point, I can use slug as is, but I've been having a problem with the slug riding over a roll crimp an tearing the hulls. So I made a punch to press a step (roll crimp ledge) into the nose. Kind of like a modified semi-wadcutter. Last pic looks like a fmj (just the lighting) about 3/8 inch of exposed lead on nose.
These slugs weigh 440 grains, I think I've got everything. Thanks D