Not recommended.
Best left to a trained factory representative.
I'm not sure why you want a two stage trigger. There are a number of aftermarket triggers available from Timney, Jard, Rifle Basix and DAYTON TRAISTER for the Ruger M 77 MKII. Most require some fitting for the safety cam. Wolf Springs also offers replacement springs that will lighten the pull slightly. BS Firearms Services
If it came with an accutrigger from savage then yes. If not you will have to install an adjustable trigger one can be purchased from midwayusa and if you follow the directions you will have no problem installing it.
The standard caliber of a biathlon rifle is .22.
a .22 caliber
A .177 caliber air rifle has very little recoil.
.223 caliber or 5.56mm.
No You could build a rifle in .306" or any other caliber but you are likely referring to 30.06. A 30.06 rifle is referred to as "30 Caliber" but to be accurate it is nominally .308"
Yes, I can. A Barrett M107 is a .50 caliber sniper rifle.
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.
The Dragunov (note corrected spelling) sniper rifle is in caliber 7.62x54mmR. This is the same caliber at the Moisin-Nagant 91/30 rifle.
50 caliber