The Box O' Truth has a pretty succinct explanation of a C&R license:surprise_i'm_armed wrote:If you had that kind of Federal license, do the firearms have to be over 100 years old? Do you need that license because the firearms are so old that they don't use regular ammo, like black powder guns?
http://www.theboxotruth.com/docs/crlicense.htm
Generally speaking, any non-auto military firearm in use prior to 1946 can qualify as a "cruffler." So Bart's comment about a $100 cruffler could mean a used, mil-surp WWII rifle.