So let's recap:
Then they are making them wrong.
Mil Spec calls for a hole that's .250". If they're drilling a hole that's .255" then they're drilling the wrong size hole. It's as simple as that.
Send them this for reference:
http://www.biggerhammer.net/ar15/cad/ar15_receiver.pdf
It's also worth noting the wedges are essentially useless for and more psychological than anything.
ref: http://www.frfrogspad.com/ar.htm
Near the bottom / word search "wedge"