4% is about the largest the tolerance range gets and for many coins it is much smaller. The ranges of current coins can be found in the law Title 31 Chapter 25 section 5112. Tolerances of uncurrent coin can be found by combing through the Statutes at Large. OR all of them can be found brought together in one place in the Coin World
Almanac by Amos Press. Copies can be found on abebooks.com for $7 and up. If you just want the tolerances drop me an email through the PM feature (click on my user name to get tom profile and select "send an email") and I'll send you a copy.