If you mean when the action is uncocked, hammer down and everything is at rest, how much movement there is is not an issue.
If you mean how much movement is OK when the trigger is pulled and the hammer is in the firing position this differs from brand to brand.
The Colt is different than any other brand of gun, in that it has Colt's famous "bank vault" lock up system.
In the Colt system, when the trigger is pulled, the cylinder is forced into a tightly locked position where there is NO cylinder movement.
This puts the cylinder chamber into perfect alignment with the barrel and insures the bullet will enter the barrel perfectly centered.
This means that the bullet isn't distorted by hitting the bore off center, and this is one reason why Pythons are famous for accuracy.
The problem with the old Colt actions is, everything depends on the action being in PERFECT adjustment.
If anything gets out of adjustment, accuracy degrades badly.
All other brands of guns, like the S&W, Ruger, and Taurus use an entirely different design.
In these guns the cylinder is ALLOWED to be loose at the moment of firing.
This allows the cylinder to align itself with the bore.
The advantage of this system is, the gun's action is much easier to build, and it can be slightly out of proper adjustment and still work well.
The down side of this is, the bullet actually does the job of aligning the chamber with the bore, and the bullet never enters the bore perfectly centered.
This slight misalignment means the bullet gets distorted and accuracy isn't as good as it could be.
The reason most revolvers use this system is, it's much cheaper and easier to build this type of action.
The old Colt action as used on the Python must be factory fitted and adjusted by a Master fitter, and this requires a considerable amount of expensive hand labor.
This hand labor is one reason why the Python is so expensive.
It amounts to having a custom built, hand fitted action, while the others are simply assembled with little fitting required.
So, all revolvers will have some cylinder looseness when the action is at rest.
All revolvers will have some cylinder looseness when the hammer is cocked.
The old Colt action alone will be tightly and immovably locked at the moment of firing.
S&W, Ruger, Taurus, and most other revolvers will have some looseness at the moment of firing.
How MUCH looseness at the moment of ignition is not something that has an actual spec.
The crucial measurement is done with a bore-chamber alignment tool known as a "range" rod.
This is a tool that slips down the barrel and is a snug fit in the bore.
The alignment between the bore and the chamber is checked by whether the range rod will smoothly enter the chambers.
How much is TOO much?
On the Colt ANY amount of looseness at ignition is too much. This means something is wrong, and the gun should be returned to the factory.
In the other brands, how much is too much is subjective.
If there seems to be a lot of looseness, compare the revolver to another revolver of the same make.
Also inspect the revolver for battering of the cylinder slots and the cylinder locking bolt.
In most cases, excessive looseness at the moment of ignition indicates a worn or abused gun.
