Cock on Open
A bolt design that cocks the firing pin as the bolt handle is lifted and the bolt opens, the standard arrangement on modern precision rifles.
In a cock-on-open action the camming surfaces compress the mainspring during the initial lift of the bolt handle, so the work of cocking is spread across the opening stroke. This is the layout used by the Mauser 98 and by nearly every contemporary hunting and target rifle built on that lineage. The shooter feels a firm but manageable lift because the energy goes into setting the cocking-piece back against the spring before the cartridge is extracted.
The practical benefit is a clean, predictable close: once the bolt is cocked on the lift, running it forward and down chambers the next round without fighting spring pressure. That smooth feed is one reason the design dominates, and it stands in direct contrast to cock on close, where the spring is loaded as the bolt drives home. Setting the firing-pin during the lift also makes a partially worked action easy to read by feel.