Best left to a good gunsmith
See the link below for the Owners Manual. Read the section "Adjusting the Trigger."
Rossi IS the maker. Rossi is currently owned by Taurus.
Adjusting the trigger on a FN Mauser involves first ensuring the rifle is unloaded and safe to handle. You typically access the trigger assembly by removing the stock. You can then adjust the trigger pull weight by turning the adjustment screw located on the trigger mechanism, being careful to make small adjustments and test the trigger pull until you achieve the desired sensitivity. Always ensure to check the safety and function after adjustments.
There were a few that do not have a standard trigger, but use a THUMB trigger. Do a web IMAGE search for Winchester thumb trigger rifle, and you will find it.
Brownells and midway have them
no
100 or so
Rossi
If you are referring to a "SET Trigger" on a rifle. The Set Trigger releases all the normal mechanisms in the action but does not release the hammer on the rifle, but it sets up the firing trigger to act like a "Hair Trigger" just barley touch the firing trigger and the rifle goes off. It's used in hunting. It is common on black powder "Hawkins Rifles."
You will have to contact Rossi or find one of their catalogs
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