Lightsped, thanks so much for posting the photo of the underside of the rifle.
When a CZ 452 has the four screw set up as yours does it indicates that it actually employs a single action screw. Here are the four screws' functions (from the muzzle):
1. this screw helps secure the barreled action via a under barrel lug that is threaded for this forearm screw (little hard to distinguish in Lightsped's photo from above - just a glint of it showing)
2. the next one secures the floor plate to the stock
3. this does the most work, it secures the barreled action to the stock by screwing into the action
4. this also helps secure the floor plate/trigger guard to the stock.
This single action screw and one barrel screw design is commonly employed by the Silhouette, the FS, the Special, the Lux, and the Varmint models.
The CZ American uses three screws consisting of two stock to action screws and one floor plate to stock screw. Thus the CZ American is intended to have a free floating barrel (some end up touching due to mass production flaws and shipping warpage). The American is probably the most inherently accurate of the breed due to this feature. But, this is not always the case.
CZ rimfire fans often obsess over methods of floating the barrel lugged designs. But, I don't. The CZ engineers and assemblers know what they are doing and any of their rimfires will shoot very well. But that being said, I think the Americans (even with their skinny barrels) are the most accurate of the lot if you have one that is truly free floated from the factory or have performed a nice clean up job yourself.
Please note these exceptions:
The 452 FS magnum rimfires and most if not all, of the magnum chambered 452 Varmint models have the two action screws.
The newer 453 (upgraded with a single set trigger design) models of the American and Varmint (both LR and magnum models) employ the two screw action.
The humble little CZ 513 Basic uses a variation the same 452 action but employs only one action screw and two floor plate screws. But, don't sell these short either as I have one that groups with the best of them.