"Loose" (usually) means with the FE attached, action closed and locked, you can feel a wiggle with shaking the gun when holding the grip. Frequently the top lever will also be to the left of mid-line.
A slight wiggle with the FE OFF is probably OK.

With the very strong top rib extension lock-up of Smith guns, the slot in the extension can be built up and then filed to tighten the action



Check out What is the advantage of the "Treble Wedge Extension Rib" Rotary Lock Bolt? in the Design and Engineering FAQ
https://lcsca.clubexpress.com/content.aspx?page_id=274&club_id=43784