If you look closely, the Griffin & Howe / Arrieta in question it has the locking stud for the hand detachable lock pin lever. It's no big deal, the lock pin lever has either been pushed a little past the proper orientation where the lock stud engages or more likely the lock pin lever needs to rotate another 320 degrees or so. Usually some effort is necessary to push the lock pin lever over the locking stud when fully seated. I normally use a small block of wood for this to save my thumb.
Arrieta adds this to their higher grade guns as should be done all H&H style hand detachable lock systems since friction alone won't always keep the lock pin tight & properly oriented with wear & wood changes over the years.
I like hand detachable locks as they provide one or sometimes 3 less screws for Bubba to bugger up on the side plates.
