And what does any of that have to do with "sporting purposes"?
I totally see where you are coming from and I TOTALLY agree. It is such a broad undefined term that it could mean whatever the hell the ATF wants to say it is.
The ATF has written a procedure for determination that is just bizarre.
They do it on a "point" system where a revolver must have a point score of at least 45. THey give points for features such as:
-1/2 point for each 1/4" over 4"
-15 points for being made of forged steel
-1 point per ounce of weight
-5 points if .357 mag "or over" (whatever the hell that means)
-5 points for adjustable sights
-5 points for "target grips" (?)
and a few others.
http://www.atf.gov/pub/treas_pub/assault_rifles/exh4.pdf
It is stupid and the GCA of 1968 needs to either be repealed ot completely rewritten!