A nice crimp will just kinda pop in place and stay closed with almost room for a dime to set in it , it is possible to apply to much pressure and push the hull side up into the crimp especially when pre crimping making the crimping part of the shell to long to fold in nice and tight . I believe what you are doing is learning the art of producing a beautiful crimp , and with a lee loader it is more about the feel . You can see where the original crimp was on the side of the hull the load must leave room to allow the finished crimp to fit down in the hull a little bit to keep it closed . As far as the slug barrel I can't help you , I buy things when I want them so I pay to much , then when I don't want it is worth much less to me . On a side note I hope you got a deal on your shotgun because I got the felling your hooked . Good choice on the Mossberg swapping barrels make them very handy , cruise ebay or gun broker for a used slug barrel .