2nd design improved a little:

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7/8-14 nut, 5/16 square stock welded, 3/16 pin, 1/4 x 1 x 6 strap iron.  Simple.  It works.  50 Beowolf shown for scale.  Lee universal decapper.

Cost:  $11 for Lee decapper.  $1.75 for the nut.  (Total material cost under $15 including die.)  Machining and setup time about 2 hours - mostly setup.

Not as gracefull as Pete's.  (Thanks Pete for the pix.)  Requres two hands to operate.