The answer lies here, if you choose to read it:
http://www.stephenhalbrook.com/tc.htmljhalcott is correct. Per BATF, the following guidelines:
Cont./Encore frame, buttstock and rifled barrel >16" = OKAY (26" min. OAL)
Cont./Encore frame, buttstock and rifled barrel<16" = NOT OKAY
Cont./Encore frame, pistol grip and rifled barrel of any length= OKAY
Cont./Encore frame only, without stock or grip, and rifled barrel of any length = OKAY
Individual States may have their own screwy addendums to the above, I dunno. Kentucky leaves me and my Contenders/Encores alone, thank God.