ok here's a beginner question..
what is meant when they say a rifle has a 2 stage trigger and either 1st or 2nd stage is adjustable??
Ahh one of my favourite topics.......
To my way of thinking a 'true' two stage trigger is one where the trigger has a light movement with a distinct stop before the trigger breaks. This first movement also alters the degree of sear engagement from considerable engagement down to a fine edge (conversely the engagement increases again if the trigger blade is released).
The available adjustments allow you to balance the amount of travel between the stages.
The AA S400 series rifles feature true two-stage triggers as does the EV2, the BSA S10 is also a true two stage unit. Many spring rifles feature true two stage triggers e.g. HW's (Rekord and Elite triggers), AA TX200/Pro-sport.
Many pcp rifles are advertised as featuring 'two stage triggers', but the majority of these are not true two stage triggers they are a pseudo two stage, whereby the trigger is actually single stage, with a trigger blade that is lightly sprung to give an impression of a two stage trigger without the alteration in sear engagement.
Hope that helps.
They say a picture can speak a thousand words.........
This image shows an S400 (two sear type) trigger mechanism in a cocked state. Notice the level of engagement between the middle and top sears highlighted in the red circle. The degree of engagement is controlled by the 1st stage adjuster screw which is located in the trigger blade (blue circle) - the sear engagement is less the further this screw is screwed in and vice versa. The overall weight of the trigger pull is controlled by the spring highlighted in the yellow circle
This image now shows the trigger with the 1st stage taken up (as when in use). Once again notice the degree of engagement between middle and top sears highlighted in red - this has now decreased to a point where further pressure on the trigger blade will release the trigger with a clean crisp feeling break. This is controlled by the 2nd stage adjustment screw (green circle) now coming into play and contacting the middle sear. The stop point felt in a two stage trigger is this adjuster contacting the sear.
Now as you can appreciate the adjustment of this screw is critical to the break of the trigger. If it is screwed too far out, the sears will disengage before a 2nd stage is felt, in effect giving a long creeping single stage pull. If it is screwed too far in the screw contacts the sear before minimal engagement occurs which in turn gives a long creepy 2nd stage as there will still be considerable sear engagement to remove before the sears disengage.
By balancing the adjustment of these two screws you can alter the length of the felt first stage.
While these photos relate to the S400 trigger, the principal remains the same for any true two stage trigger.
<span class='smallblacktext'>[ Edited Fri Mar 10 2006, 10:06AM ]</span>
Going to the other end of the spectrum, the following image is of a fake 'two-stage' trigger:
This is an extremely simple trigger, and considering the price of the rifles it is offered in, is rubbish IMO. :cursin
The bent is a simple hook (red circle) that engages a rod on the striker. Engagement is controlled by the large screw (green) bearing on the outer surface of the rifle's body tube. The alloy chassis to which the trigger blade is attached is pivoted and sprung to give the phoney 1st stage travel.