Should be marked on the barrel. If not, take it to a gunsmith.
It will be marked on the barrel.
We need the make of rifle.
The standard caliber of a biathlon rifle is .22.
a .22 caliber
You will have to tell us if you are talking about black powder or center fire.
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.
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
Not if you don't give me any information like the model? or who made it. The caliber would also help.