i was consdering shortening my barrel on my hunter class rifle from 21" to 18" or maybe even 16".

i was also looking through the rules on equipment, and can't find anything on barrel "shortness" that would disqualify the rifle from hunter class. is there a minimum barrel length?

This is pure speculation on my part, but to qualify as "hunting" rifle (for competitive purposes), wouldn't it be a "given" that it must be legal to "hunt" with? If that logic is applicable, then it would appear that the Federal legal requirement for a rifle to have a 16 inch minimum barrel would seem to apply within our (silhouette) usage.