The legality of threaded barrels in semi-auto pistols is regulated by the Guidelines Regarding the "Substantially Identical" Provision in the State's Assault Firearms Laws: http://www.state.nj.us/lps/dcj/agguide/assltf.htm A threaded barrel is one (#2) of the five named "evil" features, and the presence of any two of those would make a pistol into an "assault weapon" (i.e., illegal) in NJ. In the case of Glocks, the main issue is the "evil" feature #5; whether a pistol is "a semi-automatic version of an automatic firearm". Since Glock 18 is a select-fire machine pistol, there is an opinion that Glock 17 is "a semi-automatic version of" Glock 18, and therefore a Glock 17 with a threaded barrel would be illegal in NJ. For example, PK90 seems to be adhering to this position: http://njgunforums.com/forum/index.php/topic/29933-threaded-barrel/#entry394581 On the other hand, the NJ Gun Law Summary by vladtepes: http://njgunforums.com/forum/index.php/blog/1/entry-16-nj-gun-law-summary/ specifically states that: "A glock (which is a semi automatic pistol that has a detachable magazine ) with a threaded barrel. LEGAL" I would like to know if there has been any consensus opinion reached on this issue. This issue is complicated by the semi-mysterious existence of Glock 18: neither the US nor the EU sites of Glock have any mentioning of Glock 18. I suppose it does not imply that Glock 18 is legally non-existent in NJ. I cannot find any official technical information on Glock 18. Every available Internet source states that Glock 18 and Glock 17 are actually incompatible: http://www.cybershooters.org/dgca/prod01.htm One cannot put a Glock 18 slide on a Glock 17 frame. This seems to invalidate the claim that Glock 17 is "a semi-automatic version of" Glock 18. However, until this position is confirmed by the NJSP, I suppose one would still take a risk by using a threaded barrel in Glock 17. Another murky issue is the use of threaded barrels in, say, Glock 22. To the best of my knowledge, Glock has never made anything in .40S&W with a full auto capability. This seems to provide very strong support to the position that Glock 22 is NOT "a semi-automatic version of an automatic firearm", and therefore threaded barrels should be perfectly legal in Glock 22. However, there exist various full auto conversions (illegal in the US!) for Glock 22, or any other Glock for that matter, see, e.g. http://www.defensereview.com/select-firefull-auto-glock-22-40-sw-machine-pistol-at-the-range-sts-arms-select-fire-backplatebackplate-fire-selector-switch-for-glock-pistols-video/ and http://www.thefirearmblog.com/blog/2011/03/04/how-to-make-your-glock-fully-automatic/ I wonder if that would put at risk the use of a threaded barrel in any Glock in NJ. Of course, in my view, such a position should have no legal standing, since with sufficient ingenuity, almost any semi-automatic pistol can be converted to full auto. Any informed opinion on this issue would be highly appreciated. is there a way to get a definitive answer to these questions?