I am guessing that "drop in" refers to a barrel whose specs are loose to the point that they'll fit.
I am interested in getting a Lone Wolf 17L slide & barrel. I also really like the CCF frame. CCF recomends having any barrel (except Glock OEM and their own), "fitted" by a gunsmith.
http://www.ccfraceframes.com/faq.php
From the CCF website FAQ:
Is a gunsmith going to be able to do anything except alert me to a problem and tell me they don't fit?
I am interested in getting a Lone Wolf 17L slide & barrel. I also really like the CCF frame. CCF recomends having any barrel (except Glock OEM and their own), "fitted" by a gunsmith.
http://www.ccfraceframes.com/faq.php
From the CCF website FAQ:
Fitting of parts
13.
Will the parts from my pistol have to be fitted?
While original Glock® components are a "drop in" fit, WE STRONGLY RECOMMEND the installation of the components into the new replacement frame be performed by a certified & qualified Glock® armourer. All safety & functionality inspections MUST be performed by a certified Glock® armourer, as would be the case anytime you are re-assembling a pistol frame. Folks, please don't take shortcuts on this for the sake of convenience.
Is a gunsmith going to be able to do anything except alert me to a problem and tell me they don't fit?