Blue painter's tape? That's too thick, use a single layer of Scotch tape, if bolt closes easily, use 2, if bolt still closes easily you've got headspace issues IMHO.

On belted mag brass I creep up on sizing until I feel just a hint of resistance as bolt is nearly closed. Have never lost a case in either of my belted mags.

Sold all of my nickle plated rifle brass on eBay way back when you could still do that.