I am no expert on suppressors or the law, but by the definition of "SILENCER" by the ATF, I don't see how the Kineti-Tech shroud could be considered an NFA item just by adding a second "cap".
Just ordered the flat face barrel shroud.
http://www.kineti-tech.com/flat-face...-15-22-6-long/
National Firearms Act Definitions
Silencer
26 U.S.C. § 5845(a)(7)
For the purposes of the National Firearms Act the term Silencer is defined in 18 U.S.C. § 921(a)(24)
The term “Firearm Silencer” or “Firearm Muffler” means any device for silencing, muffling, or diminishing the report of a portable firearm, including any combination of parts, designed or redesigned, and intended for the use in assembling or fabricating a firearm silencer or firearm muffler, any part intended only for use in such assembly or fabrication.
http://www.atf.gov/firearms/guides/i...-silencer.html