The older Colt's had what Colt called their "Bank Vault" action.
The cylinder will be loose until the trigger is actually pulled, then the cylinder is locked tightly. To test the lock up, pull the trigger and hold it back, then gently test for any rotational movement of the cylinder.
All other double action revolvers like the S&W, Ruger, Dan Wesson and the newer Colt's like the Mark III and later will have rotational movement of the cylinder and they're specifically designed to allow the cylinder to be slightly loose. This allows the bullet passing from the chamber into the barrel to force the cylinder into alignment with the bore.
These guns MUST be loose, and even guns that seem to lock tightly will have enough backlash built into the action to allow the necessary movement.
On all these revolvers, pulling the trigger and checking the cylinder IS NOT a valid test for anything.